To capture your screen (or part of it) on a Mac, use one of the following commands.

  • Entire screen: Apple (Command) Key +Shift+3 

    Captures a picture of the entire desktop, which is saved on the desktop as a file called 'picture #'. This option lets you capture the whole screen. If you want just one window on your screen, you will have to edit the picture using image editing software (or use one of the other commands, instead).

  • Partial screen: Apple (Command) Key +Shift+4 

    Allows you to use your mouse to select a specific part of your desktop for capture. When your mouse pointer turns into an "x", hold down the mouse button and drag to select the part of the screen you want. When you release the button, the screenshot will capture the selected part of the screen.  Press Esc to release.

  • Selected window: Apple (Command) Key +Shift+4 then press Spacebar

    Allows you to select which window to capture.

You can also try Snapz software.

If you have Windows, read the Knowledge Base article on How do I create a screenshot in Windows?