Have you ever tried looking for the PrntScrn key on a mac? Exactly. Print Screen is a litte more difficult to pull off in OS X than in windows, but OS X's Print Screen utility is more power than its windows counterpart.
Cmd+Shift+3
Capture the entire screen.
Cmd+Shift+4
Capture using the selection tool.
Cmd+Shift+4+Space Bar
Capture using the camera tool. You can capture various parts of the interface from the dock to an entire window. This is great for including screenshots of applications.
