what should I learn or focus on as an 800?

Yes, opening principles. Look it up.

Chess Openings Resources for Beginners and Beyond...

https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond

https://www.chess.com/blog/RussBell

you should learn your tactics and understand your opponent's moves. think about the purpose of each of your moves and don't just move a piece because you don't know what to do. learn opening principles and develop your pieces in an active way. openings are not that important as a beginner just don't accept any gambits unless you know what to do. when you reach 11-1200 learning an opening may be useful but don't bother learning deep theoretical lines, the basics are fine even for my level.

Forget about openings and work on tactics and opening principles.

Always check your intended ùpbe is no blunder before you play it.
That little mental discipline alone is enough to get to 1500.

Tictacs

I'll tell you my own..

Any sound opening will work (meaning, anything but the ones that depend on gimmicks or traps).  Play around with a few of them, see which ones you like, and use that.

That said, however, it is paramount that you learn opening principles, not openings themselves, as your opponent is surely going to play things that you haven't prepared for.  

Here's a nice and short video summarizing opening principles.  Definitely worth 8 minutes of any beginners time! 

focus on learning what the optimal moves are for different openings.  Learn that you must not make idle moves, but have purpose behind your moves.  Look for moves that are both offensive and defensive in nature. multi purposed, strive to focus and not leave pieces where they can be easily captured by a one move capture, and then focus on what your opponent is going to do if you make a move, and look for a better move.