Babies begin to show readiness for solids between 4-6 months.
Signs of readiness:
Start with rice cereal mixed with formula/breast milk, 1-2 TBSP initially and then increase as your baby shows interest up to 1/2 cup.
After a week, introduce a fruit at the meals. Then continue to introduce a new fruit or vegetable every 4-5 days. Remember bananas can be constipating. Let your baby be your guide. If he/she wants to jump up to 1/2 cup of each item at each meal that is fine. And, if she/he would rather just take 1-2 TBSP of each item that is fine too.
These meals will be in addition to the bottles/nursings your baby has been taking.