Good afternoon ejbpesca,
Welcome to the Apple Support Communities!
It sounds like you'd like to know if GarageBand can be used while playing live, and we'd like to help.
Actually the best Apple app for live performance is Mainstage. It can be downloaded from the Mac App Store.
MainStage
"MainStage has something for every kind of performer. You can use all your favorite instrument and effect plug-ins from Logic Pro. Simplify setup and teardown. Sound as big as you want with backing tracks. And use all your favorite hardware controllers."
Take a look at the MainStage User Guide below for more information, including playing along to pre-recorded tracks.
The MainStage Playback plug-in in performance
"You can use the Playback plug-in to play backing tracks or other audio files while you are performing. Playback can be triggered either when you select a patch or set or by using a button or other screen control. "
Take care.