GarageBand '11: Send a song to iTunes
When you finish your project, you can send it to an iTunes playlist to play, burn to a CD, or share on the Internet.
Send a song to an iTunes playlist
Make sure the project sounds the way you want it to, and that the tracks you want to hear are not muted.
Choose Share > Send Song to iTunes.
In the Share dialog, you can add artist, playlist, and album information, and choose compression settings for the exported song.
iTunes opens, with the song added to the playlist.