Steam's backups are not that brilliant as it's supposed to create an .exe file that automatically 
restores the game but it either doesn't create one at all or it doesn't work and only restores some 
of the game.

Best method is to click "steam" within steam -> Backup and restore games..
Select the "Restore a previous backup" radio button and click next
I recommdend copying and pasting in the path to the backup file's folder as steam seems to sort 
folders in an unknown order so it's often hard to find anything but your going to have to hit enter 
and search for the expanded out folder anyway...
Click next several times...