I think he means how it will stay in place and be the same size on all screen resolutions. I don't know the name for it, but when you are sizing a gui, the numbers on the left are the numbers that will size the gui compared the screen size, and the numbers on the right will size the gui according to pixel size. As an example:
(0.5, 0, 0.5, 0) will create a gui that is half the X and Y size of the screen
(0, 0.5, 0, 0.5) will create a gui that is .5 pixels high and .5 pixels long |