Print Screen in Mac OS X

* Switch to screen that you want to capture
* Hold down Apple key ⌘ + Shift + 3 and release all
* then click on desktop
* You will see a picture file in desktop.

You can also capture Portion of screen.
* Switch to the screen that you want to capture
* Hold down Apple key ⌘ + Shift + 4 and release all key
* You see the mouse cursor change to +
* Drag mouse to select the portion capture.
* Once finish, you will see a picture file in desktop.

You can also capture Particular application window
* Switch to the screen that you want to capture
* Hold down Apple key ⌘ + Shift + 4 and release all key
* Now, You will see the mouse cursor will change to +
* Press the space bar once
* You will see the mouse cursor change to camera
* Use the camera to capture application window
* Once finish, you will see a picture file in desktop.