Q: Please~~! How do I transfer music from iMac to iPhone?

Hello VertigoPlanes,

Thanks for using Apple Support Communities.

If you'd like to send a complete GarageBand song to your iPhone in order to play it, all you need to do is share the song to iTunes, and then sync the song to your iPhone.

GarageBand Help: Share songs to iTunes

Manage content manually on your iPhone, iPad, and iPod - Apple Support

Take care,

Alex H.