How can I transfer pictures from a USB key to my Mac book air

If the USB is readable by your Mac, just open iPhoto and on the Menubar, iPhoto > File > Import to library..

If it's just a few shots, open finder and drag the photos to the desktop

plug it into the usb port it, go onto finder click it and search the files. hope this helps

You'll get the hang of it soon, it really is easy to use.

Glad to help. 🙂