Soft foods. At that age, the only "no" foods are honey (until 1 year), foods that immediate family members are allergic to, and foods that might choke him. The old rules of one new food every 3-5 days has not been shown to help with allergy identification. You can start foods in any order and even begin new foods on the same day. Just be sure they are a texture your baby can handle, starting soft then chunky.
Rice cereal. You can begin slowly introducing a 6-month old to appropriate solid foods. Rice cereal is often the first item to begin experimenting with. Always spoon feed. Avoid adding solids to a bottle. Make the consistency easy for your baby to learn to swallow solids. Once you have established there is no reaction, try oatmeal cereal. Try each food for 5 to 7 days before yoy add a new one. Then veggies!