Breast milk or formula should provide most of the nutrition for infants from birth to six months of age.
Breast milk is preferred.
Breast milk is easier to digest, provides antibodies and breast feeding is good for mother's health as well. The flavor of breast milk varies with mother's diet so baby gets used to a variety of flavors, helping her adapt to new foods later. If you have trouble getting started with breast feeding try consulting a lactation specialist. Your doctor or hospital can probably recommend one. The La Leche League is a great resource.