Screen Capture:
* Command-Shift-3: Take a screenshot of the screen, and save it as a file on the desktop
* Command-Shift-4, then select an area: Take a screenshot of an area and save it as a file on the desktop
* Command-Shift-4, then space, then click a window: Take a screenshot of a window and save it as a file on the desktop
* Command-Control-Shift-3: Take a screenshot of the screen, and save it to the clipboard
* Command-Control-Shift-4, then select an area: Take a screenshot of an area and save it to the clipboard
* Command-Control-Shift-4, then space, then click a window: Take a screenshot of a window and save it to the clipboard
Or just use Preview to do the screen capture to start with and then you can save it anywhere you want and not just on the desktop and save it as any type of image file you want as well as give it a name.