Leave the baby bird right where you found it. It is a wild bird. They are outside and survive in storms.
If it is a nestling (still bare/fuzzy), try to get it back in the nest. Don't worry that you have touched it, birds do not have an acute sense of smell, and the parents will not reject it because you touched it.
If it has feathers, it is a fledgling. Baby birds fledge (leave the nest) a few days befroe they can fly. They hop around on the ground and climb low branches until their wings are strengthened enough for flight. The parent birds continue to feed and care for the fledglings until they are self-sufficient. So if it has feathers, leave it alone!
If you must "save" the bird, then take it to a licensed wildlife rehabilitator, as you do not have the training, or the proper permits, to keep the bird. You can find a licensed rehabilitator here: http://www.tc.umn.edu/~devo0028/contact.htm
But the best thing is to leave the bird alone and stop interfering with nature.