When she starts sucking on the top part of the nipple, pull it back out, and then let her suck it in again, and repeat a few times until she sucks the whole nipple in and gets locked on. (dadsadventure.com)
This is important for breastfeeding moms as once the baby is bottle feed you don't want her to learn to suck improperly (latching on the tip of the nipple rather than on the whole nipple which is painful). (babygearhub.net)
You need to massage the whole nipple, including the areola, for fifteen minutes before moving onto the next one. (medic8.com)