The script for the Main Menu.

MainMenuScript.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
//This package contains the commands for loading different scenes
using UnityEngine.SceneManagement;
public class MainMenuScript : MonoBehaviour
{
    //This function starts the game by loading the scene with all our gameobjects
    public void StartGame(){
        StartCoroutine(StartLoadingScene());
    }
    //This function quiets the game by calling Application.Quit()
    public void QuitGame(){
        Application.Quit();
    }
    //This is a coroutine. While how it works is somewhat vague, what it does is pauses the game until the scene is done loading
    //This makes performance in terms of computing much easier
    IEnumerator StartLoadingScene(){
            AsyncOperation asyncLoad = SceneManager.LoadSceneAsync("TestScene");

            while(!asyncLoad.isDone){
                yield return null;
            }
            StopCoroutine(StartLoadingScene());
    }
}