Hopefully you will never need to restore data, however most users find that at some stage they will have to restore from backups.
Restoring works the opposite to backing up, ie Backups copy "live" data (from your hard disk) to backup media, whereas restoring copies backed up data from your backup media back onto your hard disk.
Since restoring overwrites your live data you should make sure this is really what you want to do before commencing.