Q: Restore GarageBand

Insert Disk 2 that came with your mac.  It contains the applications, such as GarageBand.

Message was edited by: shldr2thewheel--MacBook Air, I'm assuming you need an external optical drive, unless you have another computer and use Remote Disk

2011 Mac came with no external media.

You should be able to go to AppStore, and go to Purchases tab. You should be able to see iLife applications there, with "Accept" button next to them, as per Apple article:

http://support.apple.com/kb/HT4718

Are you sure that macs that were shipped in 2011 with Snow Leopard came with no disks?  I know the ones that shipped with Lion didn't, but Snow Leopard is not available as a download.  This user lists Snow Leopard in their profile.

Sorry, good point, I missed the Snow Leopard bit.

That would be 2010 MacBook Air though in that case iLife software is included on the same USB disk as operating system:

http://support.apple.com/kb/HT4399