One device hosts and gets a room code and an invite link. Up to 3 friends join from anywhere, on the same Wi-Fi or across the internet (4 players max). Send them the link, or have them open the game and enter the code.
The game tries a direct connection first, then its built-in relays (Metered and PeerJS). If those don't work, add a TURN server you have access to (from a TURN provider, or one you run yourself). Everyone in the game should add the same one. It's saved in this browser only.