If the bird has most of its feathers, it is probably learning to fly. Generally the parents will be nearby watching it and feeding as needed. You can try observing from a distance to see if any adults seem to be around. If you know where the nest is and can reach it, you can put the baby back in the nest and then watch and make sure the parents come back. If the baby does seem to be abandoned, or is in danger from cats, pick it up and keep it in a dark, warm place until you can reach a wildlife rehabilitator. You can call your local animals shelters, the zoo, vets or pet shops and most will have a number of a wildlife group. Most groups now have some type of listing online or on Facebook. Do not try to feed it. Hopefully you can find a wildlife center quickly.
These links will have more information:
Best wishes for the little guy,