If you are familiar with chess, then you probably didn't come here to learn the rules of chess. Please try some variants!
If you are not familiar with chess, then the rules are widely available on the internet, such as on Wikipedia or premier chess sites like lichess.org and chess.com.
As with other variants, you can play chess on Pychess Variants against other people or the AI. You can also set custom positions by adjusting the FEN and play games with those using standard chess rules.