There are several ways to take screenshots in Mac OS X. A screenshot is simply capturing (taking a picture) the screen of your computer or an active window. Here is a summary of all the methods you can use to capture your screen.
How to capture full screen or entire desktop
Pressing command-shift-3 will take a screenshot of your entire screen and save it on your desktop.
Pressing command-control-shift-3 will take a screenshot of your entire screen to be placed on your clipboard so that you can paste it into another program.
How to capture a portion of your desktop
Pressing command-shift-4 and then selecting an area you wish to capture will take a screenshot of an area and save it on your desktop.
Pressing command-control-shift-4 and then selecting an area will take a screenshot of an area and save it to the clipboard.
How to capture a specific window
Pressing command-shift-4-spacebar and clicking a window will capture the window and save it on your desktop.
Pressing command-control-shift-4-spacebar and clicking a window will capture the window and save it to the clipboard.
Instead of the shortcuts described above, you may use the Grab app to take screenshots. The Grab app is located in the Applications > Utilities folder. To take screenshots, launch Grab, choose the capture type from the “capture” menu: Selection, Window, Screen and Timed Screen. To learn more about Grab Utility, please read this article.