How your baby's mouth connects to your breast/chest to suck is called 'the latch'. A good latch means:
When your baby's latch is improper (sometimes called a 'poor' or 'bad' latch), sucking can be quite painful or feel like pinching on your nipple. Usually not enough of your nipple and areola are in your baby's mouth. Cracks or blisters can develop on your nipple and your baby may not receive as much milk.
If a good latch is hard to obtain or it is painful, ask for help. Support of a lactation consultant or care provider can often help you correct a latch and both make it more comfortable and improve how much milk your baby gets. See the information below on getting a good latch.