What rating systems are there?

You don't "convert" Elo to Glicko. Glicko USES Elo. Glicko is same as Elo, just with certain rating update rules. Here for active players it all comes down to K-factor = 16.

Elo meant to represent win probability. If you win 66% games against someone, you are 115 Elo higher than him. Etc. There's a direct conversion of win/loss statistic to Elo difference and back from Elo difference to win/loss prediction. All chess players in all systems are rated in Elo. Including FIDE, USCF and even chess.com and lichess. There are certain mistakes in online chess ratings and I have a separate topic about that, feel free to read my recent posts there.
Now, what is Glicko? Glicko is a system that defines how to adjust Elo of players after each game - how much you lose or gain after each game depending on your rating, opponent's rating and rating deviation (higher for new players or for players who were inactive for a while).
Besides elo and glicko