Adding commands to buttons?

I’m trying to add commands to the buttons of my game.
I want that when the button is clicked to open a new scene, I’m trying to do this much longer I can not, already tried here in the community but also found nothing to help me. I am using this script:

/ * Example level loader * /

    // JavaScript
    OnGUI function () {
    // Make the background box
    GUI.Box (Rect (10,10,100,90), "Loader Menu");
    // Make the first button. If it is pressed, Application.Loadlevel (1) will be executed
    if (GUI.Button (Rect (20,40,80,20), "Level 1")) {
        Application.LoadLevel (1);
    }

    // Make the second button.
    if (GUI.Button (Rect (20,70,80,20), "Level 2")) {
        Application.LoadLevel (2);
    }

    GUI.EndGroup ();

}

I do not know if there’s anything wrong with it, I know I have to write the command in more if I tried several ways and nothing happens when testo in the game, ie the scene does not open.
I tried also to use those scripts that are in the tutorials of unity http://unity3d.com/support/documentation/ScriptReference/GUI.Button.html more when I try to use these scripts to read and unity does not say to a semicolon at the end please explain me also how close these right script to work. thank you

There are several things wrong with this script, starting here:

OnGUI function () {

This should be

function OnGUI () {

You have them the wrong way round.

Secondly, you have an orphaned ‘GUI.EndGroup()’ call- delete it.

As for the Unity Script reference- I find it is very complete, and very very helpful. I recommend reading it more carefully.