Well, it depends what kind of bird he is. If you can zip over to your library and pick up a copy of "Care of the Wild Feathered and Furred" that will answer most of your questions.
As a last resort, you can feed most babies a mix of baby cereal and a little hamburger, but they won't eat themselves, you have to know how to feed them. Then you've got to wean them and teach them to find food on their own. You can't just feed 'em and toss 'em out.
If you haven't had the bird for long, take it back where you found it, put it somewhere safe and see if the mother is still hanging around. She'll buzz you or the bird if she is. If so, you lucked out and can split. (The "they'll smell humans and won't take care of them" is a myth.)
My strongest recommendation is to take him to a wildlife rehabilator, today. Call any vet or vet emergecny hospital and they should be able to hook you up. Don't take the bird to an animal shelter unless that's your only choice, many will just destroy baby birds, so call first and ask.
Thanks for picking the bird up, it's obvious you're a kind soul, but in the future that should be your last resort.
If the bird was in danger (e.g. in the middle of a road) you just need to move him to a tree or something. The mother was probably nearby, in the process of teaching the baby the tricks of the trade, when you found him.
Unless you know the mother is dead or baby is injured, it's best to leave the little guys where they are.
Get busy /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif