Please refer to Apple's support page for Garageband. There you will find helpful topics for GarageBand on desktop, iPads, and iPhone
Moving Pieces from Sibelius into Garage Band:
*NOTE* - Though this video is using Sibelius 7, the process is still the same in 6. As noted in this video, you can move MIDI files from Sibelius to Garage Band, but you can not go from Garage Band to Sibelius. This is one of the limitations of Garage Band. The instructor makes reference to another program called Logic. Logic and Logic Pro are more advance versions of digital recording software and are currently not loaded in this lab.