if you can, wait till 6mths. can start with anything. cereal, puree, porridge.. you can try visit this website Make Homemade Baby Food Recipes, Homemade Baby Food Recipes, Solid Food Baby Tips, Baby Nutrition & more!
for things to add into the porridge, you can look at the veg purees in that site.. just add in n mix. but then remember to only introduce 1 new food at a time n dont introduce another new food until 4 days later (4 days wait rule) in case he allergy to some of them... there are some food that is save for a 6mths baby to consume. you can check out the website. very informative..