I think F14 and F15 do brightness of your screen down and up respectively. F13 takes screenshots in World of Warcraft... 🙂
Whatever you do, don't press "Clear". It formats your hard drive.
Not sure what F16 is for. Maybe for war time.
Okay I really have no idea what "Clear" and F16 do. I guess "Clear" works on the calculator to clear the screen.