It’s an easy four-step process. 1) remove the clear nipple through the bottom Velcro flap opening. 2) slide the baby bottle through the open Velcro flap and ensure the nipple of the bottle is all the way through to the pet’s mouth. 3) secure the bottle collar around the elastic mouth making sure the nipple is fully extended. And 4) close the opening by securing the Velcro flap shut.