When you start a new game with the 'Allow Network Players' box checked then you are hosting a game that people can join. If you have the 'Internet Public' box checked then people will be able to see your game in the Join Game window. Otherwise you will have to tell people your IP address for them to join.
When you start hosting a normal game will start with just you and the computers. You will also notice a chat-area where some messages get printed out.
When somebody joins your game you will hear a sound and be told their name and IP address in the chat-area. If you want to start a new game with the new player that has joined you can type /start into the chat-area. See a list of all commands available to you as a host at Chat Commands.
The host can change the players in the game without shutting down. Open the New Game Window (Command/Control-N), set the player slots to what you want, then close the New Game Window before /start-ing the game. You can use the <no player> and <network player> options to control the available spots. Humans will also take over slots from those set to any bot, starting at the top.
To act as a Dedicated Server (host but not play in a game), guest out of the game by typing /g in the chat.
See the Private Games page for details on hosting a private or LAN game.
You can run Lux as a no-gui server from the a shell. Read this forum thread for details.
Hosting Trouble Shooting
Some tips to fix hosting issues can be found here. http://sillysoft.net/hosting/
This page is part of the Lux Guide.