This is official description about driver.
No driver necessary on MacOS which is essentially derived from UNIX/Linux. It should be plug & play.
It looks like the Air is not recognizing the Uno. Try opening a Terminal console and type
You should get a list of 'Serial Devices' connected, try the 'ls /dev/tty.* with the Uno plugged and unplugged, any difference should reveal the name of Uno port. If no difference I would suspect the cable you are using to connect the Uno. If you are able to identify the Uno port that same name should be selectable in the Arduino IDE when you open it.
Just realized Stack Exchange is not showning my answer correctly 'ls /dev/tty.' should have an asterisk after the 'dot'.