This script goes on the canvas that holds the gameplay UI elements

UIManager.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
//Because UI is a seperate package from Unity as a whole, we have to import using the using command.
using UnityEngine.UI;

public class UIManager : MonoBehaviour {
	
    //We create Text objects in our script. The text we created earlier will be dragged into this script through the editor.
    public Text HealthText;
    public Text WaterText;
    public Text HungerText;
    public Text AmmoText;
    //Because we're displaying the different stats on the player, we need a source of information. We create a Player_Manager
    //and Weapon_Parent object so we can drag them in through the editor and get the information
    public Player_Manager Player_Stats_Source;
    public Weapon_Parent Player_Weapon_Stats_Source;

	
void Update () {
	//Every frame we get the numbers from the Player_Manager and Weapon_Parent and we set the text to the different numbers
	//In this case, every frame we're setting the text to a prefix then the number, which has to use ToString() to make it text
        HealthText.text = "Health:" + Player_Stats_Source.current_Health_Level.ToString();
        WaterText.text = "Water:" + Player_Stats_Source.current_Water_Level.ToString();
        HungerText.text = "Hunger:" + Player_Stats_Source.current_Hunger_Level.ToString();
        AmmoText.text = "Ammo: " + Player_Weapon_Stats_Source.currentAmmo.ToString();
}

    
}