Baby birdddd...rescued...what to do?

i just rescued a baby bird from the middle of the road in my drive way...there was a tree nearby but he seemed to not be able to walk or anything. i put him in a box with a nest i found a while ago and some sticks and grass. someone said something about a fledging is a bird thats fully feathered and stuff and he has all his wings but he was having like diarhea on the ground and stuff soooo what should i do?: