they nest on the ground, probably best to put it back where it was found. Otherwise, put it in a box lined with a towel. Under the towel put a plastic bottle that you have filled with hot but not boiling water. 2 bottles is good so it can have its body supported, one on each side. If you have a heat pad even better. Another towel goes over the top to keep the heat in. Make sure the box is too high for him to jump out too, and out of the way of cats etc.
To feed him, raw mince mixed with cooked egg yolk and mixed with water to a slurry. Use an eyedropper and aim for the right side of the beak (its right). Tapping the side of the container may stimulate it to open its beak to be fed. it needs to be fed once an hour dawn to dusk (say 7am to 7pm) and you can tell if it is full by feeling its crop (lower part of the neck) - should be nice and bulgy after a feed.
Expect it to die anyway
they are not easy