Online multiplayer lets you play another person on a different device in real time but at least 2 people have to be in the lobby for a match to happen. Pass and play lets you play another person in real life (recommended for mobile devices). Free play lets you play chess without any turn system (all other chess rules still apply).
Your scratch account has to be at scratcher level to be able to play online multiplayer. Piece sprites by Lucas123 on: https://opengameart.org/content/pixel-chess-pieces. This took a few weeks to make. All chess rules apply/have been coded in (including: threefold repetition draw detection, insufficient material draw detection, no possible moves draw detection, illegal move detection, pawn promotions, en passant, and castling). Currently only one lobby is available but if the game gets popular I will combine all the cloud variables into one to add 9 more lobbies as each game can only have 10 cloud variables.