You can take a snapshot of the screen on an Apple MacBook Air by pressing the Shift, Command and 3 keys – this will place a PNG formatted image onto the desktop. Pressing the 4 key instead of 3 allows you to specify a portion of the screen to capture.

Alternatively you can head into the Apple logo, System Preferences, Keyboard, then Keyboard Shortcuts where you can redefine the shortcut sequences for:

• Saving full screen image to the desktop (default: Shift, Command, 3)
• Copying full screen image to the clipboard (default: Shift, Control, Command, 3, then click and drag)
• Saving selected area to the desktop (default: Shift, Command, 4)
• Copying selected area to the clipboard (default: Shift, Control, Command, 4, then click and drag)