How do I create a menu system using Unity's GUI functions?

 need to follow the Unity GUI scripting guide:

http://unity3d.com/support/documentation/Components/GUI%20Scripting%20Guide.html

For example, the following code will create a fully functional button from scratch:

function OnGUI () {
 if (GUI.Button (Rect (10,10,150,100), "I am a button")) {
  print ("You clicked the button!");
 }
}