If you are playing on a computer, , click on the Allies tab at the top of the game. This brings you to a page that will allow you to send invite requests to your friends. The more Allies you have, the easier it will be to get their help passing Staff Gates!
If you are playing on a mobile device, click on the Mailbox icon in the lower left corner of the game screen and tap the Messages icon. Then, tap the Invite button to choose from a list of friends to invite to Bakery Blitz. You will need to be connected to Facebook to invite friends.