Zoom G2.1u USB interface to record guitar

The Zoom is my floor guitar effects unit, but is also a USB interface. What do I need to record guitar into Garageband other than that, if anything? How/where do I set up the input preferences on the Mac so it reads the signal?
Related, I want to record 4-track tapes to digital. I have the cables that connect the red/white audio outs to the 1/4" input on the Zoom, then the USB to the computer. Will that work?
Thanks in advance for answering my dumb questions!