I would get a manual or find a site that actually gave you examples and directed you step by step on its use. A square has two sides, one is the thin side and one is the thicker side, they both have names, but it escapes me. Anyway, if your angle is 12/2 then one side is on the 12 and the other is the 2 and you make your steps or birdnotch or whatever.
Its great for steps or cutting the stringers and for hanging rafters and doing the knotch. I will find an article and get back with you, stay posted.
Others will jump in also, really its easy once you get the sides in order.