Read this article: http://mac.appstorm.net/how-to/music/getting-started-with-garageband-09/
Create a new song in GarageBand and give it a good name (do not leave the name as “My Song”)
Create four tracks.
Compose a one minute piece using the following guidelines:
Use only 6 different sounding loops total. Each loop must repeat in groups of 8 or 16 measures. Overlap the loops how your wish, but each loop must play by itself for at least 8 measures, there must be a place where just two loops are playing for 8 measures, a place where 3 loops are going for 8 measure, and a place where four are playing.
This composition should be one minute long. Convert your composition to mp3 and upload it using the UPLOAD link to the right.