what is a good black opening for a 500


At that level, I wouldn't get into the details of the opening yet. It is much more beneficial to play "opening principles" until at least 1000+ chess.com rating.
https://www.chess.com/blog/KeSetoKaiba/opening-principles-again
IM Levy Rozman @gothamchess recommends the London System for learning (Moves for White: 1. d4 2. Nf3 3. Bf4 and this can be played against almost any Black response).