Re: What and when..
Has your child mastered the pincer grasp (thumb and forefinger) yet? If not, then he's probably not ready for finger foods because he's going to have a hard time getting them into his mouth. If he has mastered the pincer grasp, then you can start offering him all sorts of things, as long as they are soft and in small, non-choke-hazard sizes. We started with soft stuff from a chicken soup- strings of boiled chicken, squished carrots, etc. Many people recommend introducing one food at a time, particularly if there's a history of allergy in your family. That way if your baby has a reaction, you'll know what caused it.
When you're offering finger foods, expect a big mess. Playing with food- squishing it, smearing it, flinging it- is as normal and healthy part of the experience as eating the food is.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"