buffer scene with LoadSceneAsync

Hi, i post this message cos i have a problem in LoadSceneAsync, in script reference write this:

Description
Loads the level asynchronously in the background

i search a lot on internet how to load scene and 'wait to load' but i don't find anithing... this is my code:

Code (csharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class MainMenu : MonoBehaviour {
5.     private AsyncOperation ao;
6.    
7.     void OnGUI() {
8.         if(GUI.Button(new Rect(Screen.width / 2 - 100, Screen.height / 2 - 15, 200, 30), "Load Level 1")) {
9.             ao = Application.LoadLevelAsync(1);
10.            
11.         }
12.         if(ao != null) {
13.             GUI.Box(new Rect(0, Screen.height - 40, ao.progress * Screen.width, 40), "");
14.            
15.             Debug.Log(ao.progress);
16.         }
17.     }
18. }

what i want is, load scene and wait my commant to show, it's possible? Thank's a lot
Or, Load in background, and call method when you press the button

 

Is there a checkbox in the Unity editor to make scenes load asynchronously by default instead of having to do it programmatically?