Made for someone new on Answers, all this is is a basic example of many little toolets and a pause menu was made while doing so. All was written with no helpers in a TXT doc. when run on unity to fix and arrors. Made to work with at least Unity 2018 3,3,f1 but should be usable by anything from Unity 5.5x-present as far as i am aware.

BasicPauseMenu.cs

#region Licensing
/*Free to use all are basic functions, made in the course of 2 hour's, top's! Hope u  all like it, should be pretty simple to use.*/
#endregion

#region usings
using UnityEngine;
using UnityEngine.SceneManagement;
#endregion

#region namespace

namespace ZeredaGamesEngine.Core.Controllers
{
    #region Sctipt 1 - ZeredaGamesBasicPauseMenu

    public class BasicPauseMenu : MonoBehaviour
    {
        #region class
        
        // Basic functionality of a simple pause controller
        //
        #region Variables

        [Header("ZGPauseMenuLevelManager:"), Space(1), Header("PUBLIC SETS:"), Space(1), Tooltip("Set a key code for enabling pause and disabling pause."), SerializeField]
        private KeyCode PauseKey = KeyCode.Escape;
        private static ZGPauseMenuLevelManager instance;
        [Space(3), Header("SETTINGS:"), Space(1), Tooltip("A string using the TextArea attribute"), SerializeField]
        private string SceneName = "~Select a 'SceneName'~";
        [Space, Tooltip("If True use int values *BuildIndexToLoad* to call scene otherwise use strings *SceneName* [Only in methods 'LoadNextLevel()' | 'LoadNextLevel(bool enable)', Otherwise this isn't called.]"), SerializeField, Space]
        private bool useInt = true;
        [Range(0, 10), Tooltip("Load a scene in Build Index by 'SceneName'  *in array*."), SerializeField, Space(1)]
        private int HomeScene = 0;
        [Range(0, 10), Tooltip("Load a scene in Build Index by 'int id' *in array*."), SerializeField, Space(1)]
        private int BuildIndexToLoad = 0;

        private static bool paused = false;

        #endregion

        #region Unity Generic Methods
        void Awake()
        {
            //Was in OnEnable, but since you may not want that method or OnGUI, here it is in 'Awake' instead
            AwakeSingleton();
            LoadData();
        }

        void Update()
        {
            if (Input.GetKeyDown(PauseKey))
            {
                PauseSwitch();
            }
        }
        #endregion

        #region Custom Methods

        public static void PauseSwitch()
        {
            paused = !paused;
        }

        ///<summary>Checks if paused and un-pause', checks if scene exists in build 
        ///settings, loads  Change "{} 's to view in code."scene if is, logs and exception
        ///with a new message explaining the error. </summary>
        public void LoadScene(string sceneName)
        {
            if (Equals(SceneManager.GetSceneByName(sceneName), sceneName))
            {
                if (paused)
                    OnUnpause();
                SaveData();
                SceneManager.LoadScene(sceneName);
            }
            else
                Debug.LogException(new System.Exception("Scene does not exist in the build index"));
        }

        ///<summary>Checks if paused and un-pause', checks if scene exists in build 
        ///settings, loads  Change "{} 's to view in code."scene if is, logs and exception
        ///with a new message explaining the error. </summary>
        public void LoadScene(int buildIndexToLoad)
        {
            if (Equals(SceneManager.GetSceneAt(BuildIndexToLoad).buildIndex, buildIndexToLoad))
            {
                if (paused)
                    OnUnpause();
                SaveData();
                SceneManager.LoadScene(buildIndexToLoad);
            }
            else
                Debug.LogException(new System.Exception("Scene does not exist in the build index"));
        }

        /// <summary>
        /// Loads the Next Scene
        /// </summary>
        public void LoadNextScene()
        {
            if (paused)
                OnUnpause();
            SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex + 1);
        }

        /// <summary>
        /// Loads the Next Scene by inspector "BuildIndexToLoad" Or "SceneName"
        /// </summary>
        /// <param name="UseInt"></param>
        public void LoadNextScene(bool UseInt)
        {
            if (UseInt)
            {
                if (Equals(SceneManager.GetActiveScene().buildIndex, BuildIndexToLoad))
                {
                    if (paused)
                        OnUnpause();
                    SaveData();
                    SceneManager.LoadScene(BuildIndexToLoad);
                }
                else
                    Debug.LogException(new System.Exception("Scene does not exist in the build index"));
            }
            else {
                if (Equals(SceneManager.GetSceneByName(SceneName), SceneName))
                {
                    if (paused)
                        OnUnpause();
                    SaveData();
                    SceneManager.LoadScene(BuildIndexToLoad);
                }
                else
                    Debug.LogException(new System.Exception("Scene does not exist in the build index"));
            }
        }

        /// <summary>
        /// Quit's the application Able To Call Ditrectly From Script
        /// </summary>
		public static void QuitApplication()
        {
            Application.Quit();
        }

        /// <summary>
        /// Quit's the application Used as a button.
        /// </summary>
		public void OnQuitApplication()
        {
            QuitApplication();
        }

        /// <summary>
        /// Last thing the script does. (Run's save sequance also)
        /// </summary>
        void OnDisable()
        {
            SaveData();
        }

        /// <summary>
        /// Run's save sequance
        /// </summary>
        void SaveData()
        {
            //SaveData.Save(Player.Id, Player.PlayerName);
        }

        /// <summary>
        /// Run's load sequance
        /// </summary>
        void LoadData()
        {
            //SaveData.Load(Player.Id, Player.PlayerName);
        }

        /// <summary>
        /// Pauses the player
        /// </summary>
        void OnPause()
        {
            if (paused)
            {
                Time.timeScale = 0.0f; //Maybe some more data?? That's up to you.
                AudioListener.volume = 0.0f;
                Cursor.visible = false;
            }
            else
                Debug.Log("Game Is Paused = " + paused);
        }

        /// <summary>
        /// Un-pauses the player
        /// </summary>
        void OnUnpause()
        {
            if (paused)
            {
                Time.timeScale = 1.0f; //Maybe some more data?? That's up to you.
                AudioListener.volume = 1.0f;
                Cursor.visible = true;
            }
            else
                Debug.Log("Game Is Paused = " + paused);
        }

        #endregion

        #region Internal Singleton
        public bool SetDontDestroyOnLoad = true;

        public static ZGPauseMenuLevelManager Instance
        {
            get
            {
                if (instance == null)
                {//in case not awake yet
                    instance = FindObjectOfType<ZGPauseMenuLevelManager>();
                }
                return instance;
            }
        }

        void AwakeSingleton()
        {
            // if the singleton hasn't been initialized yet
            if (SetDontDestroyOnLoad)
            {
                if (instance != null && instance != this)
                {
                    Debug.LogError("Duplicate singleton " + this.gameObject + " created; destroying it now");
                    Destroy(this.gameObject);
                }

                if (instance != this)
                {
                    instance = this;
                    DontDestroyOnLoad(this.gameObject);
                }
            }
            else {
                instance = this;
            }
        }
        #endregion

        #region OnGUI Extras

        // Basic functionality of a simple pause Menu
        // Extra GUI Menu HeHe this was actually pretty fun to make \/  \/

        #region GUIVariables
        private static bool EnableOptions, DropDownMenu, DropDownMenu2;
        [SerializeField, Header("GUI Content Info:"), Space, Tooltip("When enabled GUI Method calls. 'ToggleButtonGUIContent'")]
        private bool UseGUIContent = false;
        [SerializeField, Tooltip("When 'UseGUIContent' is enabled, changed GUI info on the toggle button in menu, reason is i wanted to add a tool tip to it. Works same idea for anywhere else, but would need a bunch of variables for each location so an array or preferrably a List of content is best.")]
        private GUIContent ToggleButtonGUIContent;
        [SerializeField, Space(1), Tooltip("Used to controll weather you would like to use a custom GUI style or not.")]
        private bool UseGUIStyle = false;
        [SerializeField, Space(1), Tooltip("Similar method applies here as the 'ToggleButtonGUIContent', when 'UseGUIStyle' is enabled, but this works accross many areas not just 1, i'm using it to control font,fontSize, If the text can scale and word wrap.")]
        static GUIStyle YourGUIStyle = new GUIStyle();
        [SerializeField, Tooltip("How big is the font going to be. what looks good to you?.")]
        private int FontSize = 17;
        [SerializeField, Space(1), Tooltip("Select the font for all text in menu.")]
        private Font SelectedFont;
        [SerializeField, Space(1), Tooltip("Make the GUItext have word wrap.")]
        private bool wordWrap = false;
        [SerializeField, Space(1), Tooltip("Make the GUItext scale in height.")]
        private bool expandHeight = false;
        [SerializeField, Space(1), Tooltip("Make the GUItext scale in width.")]
        private bool expandWidth = false;
        [SerializeField, Space(1), Tooltip("Set a fixed height for all texts when using 'UseGUIStyle'.")]
        private float fixedHeight;
        [SerializeField, Space(1), Tooltip("Set a fixed width for all texts when using 'UseGUIStyle'.")]
        private float fixedWidth;

        #endregion

        /// <summary>
        /// First thing the script does. (Preferrably put LoadData(); here instead of "Start();")
        /// </summary>
        private void OnEnable()
        {
            // Uncomment to use delete and from awake.
            //AwakeSingleton();
            //LoadData();
            YourGUIStyle = new GUIStyle();
            YourGUIStyle.font = SelectedFont;
            YourGUIStyle.fontSize = FontSize;
            YourGUIStyle.stretchHeight = expandHeight;
            YourGUIStyle.stretchWidth = expandWidth;
            YourGUIStyle.wordWrap = wordWrap;

            if (YourGUIStyle.stretchHeight)
            {
                YourGUIStyle.fixedHeight = fixedHeight;
            }

            if (YourGUIStyle.stretchWidth)
            {
                YourGUIStyle.fixedWidth = fixedWidth;
            }
        }

        /// <summary>
        /// Updated the Script GUI on the screen.
        /// </summary>
        void OnGUI()
        {
            //if Paused
            if (paused)
            {
                //Make quit game button
                if (UseGUIStyle)
                {
                    // Make a title in your menu
                    GUI.Box(new Rect(Screen.width / 2 - 540, Screen.height / 2.1f - 20, 270, 178), "Paused", YourGUIStyle);
                    // Load by int or string?
                    if (UseGUIContent)
                        useInt = GUILayout.Toggle(useInt, ToggleButtonGUIContent);
                    else
                        useInt = GUILayout.Toggle(useInt, "Use String or Int to call a scene.");
                    //Make a Main Menu
                    if (GUI.Button(new Rect(Screen.width / 2 - 540, Screen.height / 1.5f - 100, 270, 50), "Main menu", YourGUIStyle))
                    {
                        if (useInt) { SceneManager.LoadScene(HomeScene); }
                        else { SceneManager.LoadScene(SceneName); }
                    }
                    //Make an options button
                    if (GUI.Button(new Rect(Screen.width / 2 - 540, Screen.height / 1.5f - 50, 270, 50), "Options Menue", YourGUIStyle))
                    {
                        // Enables other options menu
                        if (DropDownMenu == false)
                        {
                            DropDownMenu = true;
                            DropDownMenu2 = false;
                        }
                        else {
                            DropDownMenu = false;
                            DropDownMenu2 = false;
                        }
                    }
                    //Make a Quit Button
                    if (GUI.Button(new Rect(Screen.width / 2 - 540, Screen.height / 1.5f + 0, 270, 50), "Quit Game", YourGUIStyle))
                        QuitApplication();
                }
                else {
                    // Make a title in your menu
                    GUI.Box(new Rect(Screen.width / 2 - 540, Screen.height / 2.1f - 20, 270, 178), "Paused");
                    // Load by int or string?
                    if (UseGUIContent)
                        useInt = GUILayout.Toggle(useInt, ToggleButtonGUIContent);
                    else
                        useInt = GUILayout.Toggle(useInt, "Use String or Int to call a scene.");
                    //Make a Main Menu
                    if (GUI.Button(new Rect(Screen.width / 2 - 540, Screen.height / 1.5f - 100, 270, 50), "Main menu"))
                    {
                        if (useInt) { SceneManager.LoadScene(HomeScene); }
                        else { SceneManager.LoadScene(SceneName); }
                    }
                    //Make an options button
                    if (GUI.Button(new Rect(Screen.width / 2 - 540, Screen.height / 1.5f - 50, 270, 50), "Options Menue"))
                    {
                        // Enables other options menu
                        if (DropDownMenu == false)
                        {
                            DropDownMenu = true;
                            DropDownMenu2 = false;
                        }
                        else {
                            DropDownMenu = false;
                            DropDownMenu2 = false;
                        }
                    }
                    if (GUI.Button(new Rect(Screen.width / 2 - 540, Screen.height / 1.5f + 0, 270, 50), "Quit Game"))
                        QuitApplication();
                }
                if (DropDownMenu)
                {
                    if (GUI.Button(new Rect(Screen.width / 2 - 315, Screen.height / 2 + 0, 230, 50), "Other Menu "))
                    {
                        if (!Equals(DropDownMenu2, false))
                        {
                            DropDownMenu = true;
                            DropDownMenu2 = true;
                        }
                        else {
                            DropDownMenu = false;
                            DropDownMenu2 = false;
                        }
                    }
                    if (GUI.Button(new Rect(Screen.width / 2 - 315, Screen.height / 2 + 50, 230, 50), "Options"))
                    {
                        EnableOptions = !EnableOptions;
                    }
                    if (EnableOptions)
                    {
                        // So Some GUI Options
                    }
                }
                if (DropDownMenu2)
                {
                    if (GUI.Button(new Rect(Screen.width / 2 - 315, Screen.height / 2 + 100, 230, 50), "Facebook"))
                    {
                        GameObject go = GameObject.FindWithTag("Facebook");
                        if (!Equals(go, null))
                            gameObject.SetActive(true);
                    }
                    if (GUI.Button(new Rect(Screen.width / 2 - 315, Screen.height / 2 + 150, 230, 50), "Twitter"))
                    {
                        GameObject go = GameObject.FindWithTag("Twitter");
                        if (!Equals(go, null))
                            gameObject.SetActive(true);
                    }
                    if (GUI.Button(new Rect(Screen.width / 2 - 315, Screen.height / 2 + 200, 230, 50), "Email"))
                    {
                        GameObject go = GameObject.FindWithTag("Email");
                        if (!Equals(go, null))
                            gameObject.SetActive(true);
                    }

                    if (GUI.Button(new Rect(Screen.width / 2 - 315, Screen.height / 2 + 250, 230, 50), "Net Browser"))
                    {
                        GameObject go = GameObject.FindWithTag("WebBrowser");
                        if (!Equals(go, null))
                            gameObject.SetActive(true);
                    }
                }
            }
        }

        #endregion
        
        #endregion
    }

    #endregion
    
    #region Script - 2 SaveData
    
    public static class SaveData{
        public static List<string>PlayerNamesList = new List<string>();
        public static List<string>IdList = new List<string>();
        public static List<bool>ConnectedPlayers = new List<bool>();
        
        public static void Load(string name, int id){
        
        }
        
        public static void Save(string name, int id){
        
        }
        public bool DisplayWarning;
        public static void OnEnable(){
            for(int i=1;i<IdList.Count:i++){
                if(i==Player.PlayerID){
                    if(ConnectedPlayers[i]==true){
                        DisplayWarning=true;
                        return;
                    }else{
                        // Only storing there user name id and if they are connected. servers should handle the rest
                        Player.PlayerName=PlayerPrefs.GetString("UserName"+i);
                        Player.PlayerID==PlayerPrefs.GetString("UserID"+i);
                        Player.PlayerIndex=i
                        Player.Connected=true;
                        PlayerNamesList[i]=Player.PlayerName;
                        IdList[i]=Player.PlayerID;
                        ConnectedPlayers[i]=Player.Connected;
                    }
                }
            }  
        }
        public static void OnDisable(){
            // Only storing there user name id and if they are connected. servers should handle the rest
            PlayerPrefs.SetString("UserName"+PlayerName.PlayerIndex,Player.PlayerName);
            PlayerPrefs.SetString("UserID"+PlayerName.PlayerIndex,Player.PlayerID);
            PlayerName.Connected=false;
            PlayerNamesList.Remove(Player.PlayerName);
            IdList.Remove(Player.PlayerID);
            ConnectedPlayers[PlayerName.PlayerIndex]=PlayerName.Connected;
        }
    }
    public static class Player{
        public static string PlayerName
        public static int PlayerIndex
        public static string PlayerID;
        public static bool IsConnected;
    }
}
#endregion