I found a baby bird! what to do?

Okay the best thing you can do for the bird is keep it warm. Maybe put blankets at the bottom of the box or where you are putting it. Put it NEAR a heater, or heat lamp. Also leave some bird seed if you have some. Or give it some small fruit or berry slices. Maybe go pick some leaves and put it in the box or where you are keeping it to make it comfortable. Be slow around it. Also keep an eye on it. Take it outside and watch it when the weather clears up and when the parents are back. If it can fly and walk around i would suggest its fine out there.