How to take a screenshot of your entire screen
- Press Shift-Command (⌘)-3.
- Find the screenshot as a .png file on your desktop.
How to take a screenshot of a window
- Press Shift-Command-4. The pointer changes to a crosshair.
- Press the Spacebar. The pointer changes to a camera.
- Move the camera over a window to highlight it.
- Click your mouse or trackpad. To cancel, press the Esc (Escape) key before you click.
- Find the screenshot as a .png file on your desktop.
You can find alternative ways of taking a screenshot on Mac here.