Do you think the Apple keyboard doesn’t have a print-screen function in OS X? You would be wrong then. It actually has more than Windows XP. Use any of the following commands to put a PDF on your desktop. (Note: If you hold down the Control key during the above commands the image is copied to the clipboard, rather than creating a PDF.)
CMD + Shift + 3
This will take a screenshot of your entire screen.
CMD + Shift + 4
This will bring up a selection tool so you can make a rectangular screenshot of a certain area.
CMD + Shift + 4 + Space Bar
This turns your cursor into a camera. Use to take a picture of the Dock,or a window and it will crop the background automatically for the resulting image.