If it seems that players are unable to join your server after starting it from the “Host server” menu, you may have to setup port forwards on your router in order to let incoming connections through. We’re working on an alternative solution to remove the need for port forwarding, but for now this is how you can do it:

On many router models you can access the settings by navigating to http://192.168.1.1/ using your web browser, finding the port forwarding settings (sometimes called “application sharing”) and forwarding one of the ports using the following settings:

Game port (used to communicate with clients)
Service/Application: barotrauma
External Port: The port you have selected for your server (27015 by default)
Internal Port: The port you have selected for your server (27015 by default)
Protocol: UDP

Query port (used to communicate with Steam)
Service/Application: barotrauma
External Port: The port you have selected for your server (27016 by default)
Internal Port: The port you have selected for your server (27016 by default)
Protocol: UDP

The exact steps for forwarding a port depend on your router’s model, but you may be able to find a more detailed port forwarding guide for your particular router on http://www.portforward.com or by googling your router model + port forwarding.

If you are playing the old, non-Steam legacy version, you only need to forward the game port (14242 by default).