Pick a time control (bullet, blitz, rapid, classical or no clock) and wait for someone to sit across from you. Nobody around? Play the robot. Timed games are rated with Glicko-2, with a separate rating for each time control, and the top players go up on the boards inside. After a game you can go back through it with Stockfish (not always cz of limitations) telling you exactly where you blundered. Have fun