Handle bar rotates on its own. Can’t screw the screw all the way down
That’s a tension bolt for a quill stem I think. Is there a wedge shaped piece floating around inside the fork now? You can fish it out with that bolt or maybe flip the bike upside down.



The last few mm of the bolt look stripped which may or may not be an issue. The small bend in the bolt shouldn’t be an issue. 

Try cleaning everything then reinstalling with a dab of grease on the threads and the interface between wedge and stem. Don’t over tighten the bolt.

You can buy a new quill stem at your local bike store or online for not much $. You’ll need to get the right size for your fork diameter.