It's great that you're so creative, and your Mac thinks so too. But what good does it do you if no one notices? Fortunately, you can share your GarageBand jewels with your soon-to-be adoring public in several ways.
You can send a song or an iPhone ringtone you created in GarageBand directly to a playlist in your personal iTunes library.
Choose Share→Song to iTunes, and choose the compression (typically, AAC Encoder) and audio settings you want. Then click Share. You can also export the song to a disk or burn it to a CD (assuming that you have access to a CD burner). And you can whisk it off to SoundCloud, a popular third party online destination for audio files. (You'll have to sign into your SoundCloud account.)
In the case of a ringtone, choose Share→Ringtone to iTunes.
You can send a single track (or group of tracks) instead of a complete song to iTunes. Just mute all the tracks you don't want to send before sending the ones you do want.
You don't have to export your ditty to iTunes. You can send it as an audio file by choosing Share→Export Song to Disk.
Still another option for your composition is burning the song to a recordable CD. Just place a blank disc in your Mac's optical drive, choose Share→Burn Song to CD, choose the settings you want, and click Burn.
You can burn only one song to a CD this way. To burn multiple songs, create or add them to an iTunes playlist first and then burn the playlist to a CD via iTunes.
Whichever way you go, remember — the show must go on. Your fans are waiting.