At 3 months
First talk to your pediatrician. Babies don't need anything but breast milk or formula until 5 - 6 months. Solid food is an add on to the main source of nutrition. Introduce vegetables before fruits, so that your baby will be more likely to accept them, you can start with vegetables such as green peas, acorn squash or sweet potatoes. Then for fruit try apples, pears and bananas. Remember to try one food at a time spaced at least 3 days apart in case of allergy sensitivity.