For a start, offer solids only after milk feeds. Give some time for the milk to be digested, maybe 30 mins, then offer the solids. Abt 1 tablespoon is fine, and gradually increase to 2-3 tbsp over the next few weeks. Depends on baby's appetite too. Milk is still their primary source of food.
Your solid shouldn't replace milk feed. It's just to introduce your baby to food