I've been using GarageBand since I joined the forum. First, I used it on an iPad, then on a Mac. I just use it for recording BGU lessons, and the occasional VJR stuff. I'm no Mac/Garageband expert, but it's so easy, I don't think you have to be. That's all I had to do was get an interface for the guitar (an Apogee Jam) and plug it in to the Mac (USB). If you want to sing, you may want to consider a more robust interface with 2 inputs - Mic & Guitar.
The "DAW" is pretty easy to use. The cool thing about Macs is that everything is just drag-and-drop. So you can easily grab an MP3 (after downloading it from the VJR) and pop it into one track and then record your guitar on another track. GarageBand has a bunch of "toys" (models of amps and effects) to play with, but I haven't explored a lot of it. I think cowboy bob’s suggestion of the tutorials is a good one, though I’ve never done the midi stuff.
I think GarageBand is a good move for a total beginner. It was for me. I sometimes wonder if I could make way better recordings with "pro" equipment, then I slap myself and remember who's playing!
I agree with papa, once you get an interface, this won't take more than a week!