Babies breathe to exercise their lungs. They cry to communicate with you. They cry (without tears until after the first month or two) because they are hungry, in pain, tired, cold, need a clean nappy, are sick or want physical contact. If you respond quickly to what your baby is crying about, the crying stops.
Some people advise that you let your baby cry herself to sleep. Generally, this is not a good idea. Your newborn needs you to respond quickly to her cries in order to develop strong and lasting feelings of safety, security and self-confidence. You should trust your own instinct when your baby cries pick her up. You cannot spoil her if she is crying because she is distressed.
In newborns, crying is a late sign of hunger. It is best to feed your baby before she starts crying so that she does not become so upset she cannot take the breast or bottle. Try to calm her by holding her firmly or wrapping her tightly in a blanket before you feed her. If a baby is overtired and overstimulated, she may not be able to relax enough to get to sleep.