Each capture sequence below saves a file to your desktop, unless you add a Control key to any sequence which will give you the capture as a copy to the clipboard.
Also see the Grab utility for more complex captures, including recording desktop activities.
- Entire desktop - Cmd + Shift + 3
- Specific area - Cmd + Shift + 4, gives crosshairs that can be positioned for click and drag
- Single window - Cmd + Shift + 4 + Spacebar, gives a camera that highlights windows to be captured