Two-player free hunting
The official cooperative mode is free hunting for two players. It should not be treated as a shared version of the complete single-player campaign. Password-protected games, larger player counts and other expanded multiplayer features belong to future plans unless a later update explicitly adds them.
How progress and populations work
Single-player and multiplayer have separate worlds and animal populations. The FAQ describes progress within multiplayer sessions as saved, while a Persistent World shared or synchronized across different player sessions is still planned. Do not treat this as one long-term single-player herd-management world jointly owned by two players.
Prepare before joining
Finish the tutorial on both accounts and use matching game versions. In the Multiplayer room-list flow, check NAME, MAP and PLAYERS; a 1/2 room has space, while 2/2 is full. After loading, check your carried equipment in Storage rather than assuming the single-player loadout has followed you.
The room-list interface was demonstrated in Early Access, so follow the labels shown by your installed version. Loading to 100% alone is not a useful final check: confirm that your character or equipment screen is usable after joining.
Invitation and synchronization issues
Patch 1.2 lists a fix for a brand-new save becoming stuck after accepting an invitation. The known-issues page also retains a tutorial-related invitation warning, so completing training first remains the conservative preparation step.
For short-lived desynchronization, try moving closer to the host or waiting. If a client cannot interact with a parking sign or door, reconnecting is the official suggested workaround. Treat crashes and disappearing animals separately; reconnecting is not a guaranteed cure for every multiplayer problem.