here is what i found.

One way to take screen shots is to invoke Mac OS X's built-in screen capture capability by pressing the following keyboard shortcuts:

Command-Shift-3: Immediately takes a picture of the entire screen.
Command-Shift-4: Changes the cursor into crosshairs. Drag the crosshairs over a section of the screen, then release the mouse button to capture the shaded area.

By default, screen shots captured in this fashion are saved as PNG image files on the Finder's desktop, sequentially named Picture 1, Picture 2, etc. To copy the image to the Clipboard instead, hold down the Control key when you press the appropriate keyboard shortcut.