If you must start a bottle, do so when your baby is at least 2 months of age. Don't be surprised if at first your baby refuses to take a bottle of breast milk. A breast fed baby simply knows instinctively is not to take milk from a bottle when his mother is right there. You should introduce solid foods when your baby is 6 months old. Breast milk or a powdered milk formula should be continued till your baby is 1 year old.
Most babies start with 'daliya' - a simple rice based cereal which is easy to digest.
You need to mix it with enough liquid to make a thin semi liquid - semi solid mass that is easy to swallow. Sit the baby up in your lap and give him one tiny spoonful. Remember this is the first time he will be taking a solid. It will take some getting used to the idea of eating his food rather than drinking it. If he gags or rejects the food, he may not be ready.