Before you try nursing in public, watch how other moms do it. Practice at home in front of a mirror. First try nursing in front of people with whom you feel at ease. When going out in public, wear the right kind of clothes - loose shirts that can be pulled up or unbuttoned from the bottom. Wearing sweaters or jackets can also help to cover you.
Some women like to drape a blanket over their shoulders before nursing.
You'll be surprised. Many people will think your baby is just sleeping in your arms. Pregnancy makes some women's breasts sag whether they breastfeed or not. A lot depends on the size of the woman's breasts, her muscle tone, and heredity. I have small breasts.