How to Take a Screenshot on a MacBook

There are several keyboard combinations that can be used to take screenshots in Mac OS X. The SystemUIServer process handles these commands.

Take a picture of the whole screen
Press at the same time Command⌘-Shift-3

Take a picture of part of the screen
Press at the same time Command⌘-Shift-4, then drag to select the area you want in the picture.

To cancel, press Escape.

Take a picture of a window, a menu, the menu bar, or the Dock.
Press ⌘-Shift-4, then press the Space bar. Move the pointer over the area you want so that it’s highlighted, then click.

To drag to select the area instead, press the Space bar again. To cancel, press Escape.

Screen shots are saved as files on the desktop. If you want to put the screen shot in the Clipboard, rather than create a file, hold down the Control key when you press the other keys. You can then paste the picture into a document.

You can also take pictures of the screen using the Grab application (in the Utilities folder).

Some applications, such as DVD Player, may not let you take pictures of the screen.
Source(s):
Grab Help

Summary:

  1. Command-Shift-3: Take a screenshot of the screen, and save it as a file on the desktop
  2. 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

In Leopard and later, the following keys can be held down while selecting an area (via Command-Shift-4 or Command-Control-Shift-4):

Space, to lock the size of the selected region and instead move it when the mouse moves
Shift, to resize only one edge of the selected region
Option, to resize the selected region with its center as the anchor point