does a macbook air have a right-click?

Yes, Look in System Preferences > Trackpad > Secondary click

Edit: For additional options, click the down arrow next to the click or tap with two fingers.

Tap the trackpad with two fingers.

Or you can hold down the CONTROL key while clicking normally.

As noted, yes you can do it a number of ways. The "one button" concept goes back to the original Macs and to this day Apple doesn't ship with dual buttons. However there are right click options throughout the system.

As well, if you connect a mouse with two buttons you'll also get a right click option.

@captfred: THANK YOU for this answer. I just applied the security update from today to my 2013 MBA and all of a sudden I couldn't right-cick on the trackpad and it was driving me crazy. For some reason the setting reverted to the click or tap with two fingers, which I never had used.