This picture indicates how to identify a nestling from a fledgling. Why is this important?
Nestlings should be in a nest.
If you find a nestling on the ground you can locate the nest and put it back inside. If the bird continually is rejected from the nest it can mean the parents aren’t feeding them or they sense a defect and have ostracized him for a reason.
If it’s a fledgling then it’s SUPPOSED to be on the ground!
Baby birds need to learn to fly on the ground and to build up muscle strength. The parents locate them and continue to feed them. The best thing to do with a fledgling is to put him in a bush where he can safely hide and then leave him alone so the parents can find him without the predator (you) lurking.