Never tried Autoglym glass polish.
I did however used 1Z glass polish but it's been discontinued, so I just ordered 1L from the States.
If we're talking about the same procedure, then you use it like on a painted surface. Flex at speed 6, PC or UDM won't do much. Use a yellow pad or orange, but you're better with the yellow.
Do this procedure for the windshield. For your side windows and rear window use a lower speed and avoid heating the glass too much or it will go kaput on you.