Check out example codes for "exit game unity". It will help you in understanding the concepts better.

Code Example 1

//Quit/Stop Game
Application.Quit();

Code Example 2

using UnityEngine;
using System.Collections;// Quits the player when the user hits escapepublic class ExampleClass : MonoBehaviour
{
    void Update()
    {
        if (Input.GetKey("escape"))
        {
            Application.Quit();
        }
    }
}

Code Example 3

//C#
 public static class AppHelper
 {
     #if UNITY_WEBPLAYER
     public static string webplayerQuitURL = "http://google.com";
     #endif
     public static void Quit()
     {
         #if UNITY_EDITOR
         UnityEditor.EditorApplication.isPlaying = false;
         #elif UNITY_WEBPLAYER
         Application.OpenURL(webplayerQuitURL);
         #else
         Application.Quit();
         #endif
     }
 }

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