And more importantly, how do you retrieve it? For example, if I download a backing track that I want to import into garage band, how do I import it and where do I import it from?
I normally use GoodReader to import all my mp3 tracks. They then end up in the GoodReader filespace but I can use 'Open in' to transfer them to other apps that are capable of processing mp3 tracks.
I'm not even sure you can import mp3 into GarageBand. I seem to remember an article saying an update will allow this, but I don't know if that update has happened yet. At least I can't find any way to do it. The usual File Share route in iTunes does not work.
Hmm, just looked at the last update notes. I says it will import AIFF, WAV, and CAF audio files. Nothing about mp3.
Try converting your audio track to one of those three, then use the File Share section in itunes and see if you can import it that way.