To open the camera on your MacBook Air, you'll need to use the Photo Booth app, which comes pre-installed on your device. Simply click on the Launchpad icon, and then select Photo Booth from the list of apps. Easy peasy, right?
Alternatively, you can also use the Spotlight search to find the Photo Booth app. Just press Command + Space to open the search bar, type in "Photo Booth", and voilà! The app will appear, and you can start snapping away.