For Example: “new Rect(10,10,20,20)“
This would mean that the button starts at (x10) and (y10) and ends at (x20) and (y20),
So the button will have the size of 10 by 10 pixels
This can be used with the button and you will and up with:
if (GUI.Button(new Rect(10,10,20,20), GUIContent ))
{
//Do this
}