1) Each "real" track has tracks within them called Virtual Tracks. So, if track 5 is a track for your guitar solo or something, you can record multiple takes without deleting your other ideas. It stores the other takes on virtual tracks, which aren't played during playback. Once you have recorded different takes trying different things, you can choose one for the final mix. Or, you can take different chunks of each vitrual track to create the final track. I hope that isn't confussing. There is probably a more thorough explanation in your owner's manual.
2) Yes. You just use the 1/4" jack on one of the two channels to plug your guitar into.