how to make a main menu button

I know how to make a main menu with functioning buttons, but I can't make a quit button, even though I'm just using the same-ish script with a different int.

My quit code:

 using UnityEngine;
 using System.Collections;
 
 public class QuitConfirmation : MonoBehaviour
 {
 
     public void LoadScene(int level)
     {
         Application.LoadLevel(level);
     }
 }

My load code:

 using UnityEngine;
 using System.Collections;
 
 public class Loading : MonoBehaviour {
 
     public GameObject loadingImage;
 
     public void LoadScene(int level)
     {
         loadingImage.SetActive(true);
         Application.LoadLevel(level);
     }
 }

I have My main menu as 0, my first level as 1, my second as 2, and my third as 3. Basically I don't have an image that says "Loading... Your selected map will appear shortly..."