Where does GUI end up?

I know GUI is usually stated with 4 numbers, if(GUI.Button(Rect(XXX,XXX,XXX,XXX) but i have no idea which places mean what. Like which one is height? width? X or Y?

I have attached a photo of where i want a rectangle. Can you please tell me the estimated coordinates of the very top most rectangle and what goes where when making GUI buttons?

I am Using a 1920 x 1080 resolution screen aka 1080p, Im not sure if that matters.