How do I convert a Garage Band song file into a WAV or mp3 format?

Use the Share Menu > Export to disk.

Uncheck Compress for full-resolution file (aiff, similar to WAV).

Or, check Compress and select Mp3 encoder to generate an Mp3.

(edit: HT's post wasn't up before I posted!)

kaoblues wrote:

How do I convert a Garage Band song into [...] a WAV file

use the Share menu to export, uncheck the compress dialogBox, and then use iTunes to create the WAV file:

http://www.bulletsandbones.com/GB/GBFAQ.html#converttowav

(Let the page FULLY load. The link to your answer is at the top of your screen)

kaoblues wrote:

How do I convert a Garage Band song into [...] an mp3?

use the Share menu to export, tick the Compress checkBox, pick "mp3" from the popUp menu