The Gnocatan client program is "gnocatan". When you run this program, you will be presented with the connect dialog.
Using the connect dialog, you identify the game which you wish to join. This dialog is automatically invoked when you start gnocatan. If the initial connection fails, you can invoke the dialog from the Game/Connect menu, or by using the Ctrl-C keyboard shortcut.
You can manually specify the game that you wish to join by entering the server host and port in the Server Host and Server Port fields in the lower half. The client also remembers server/port/username combinations you used recently. You can recall them quickly with the Recent Servers button at the bottom.
Alternatively, you can enter the name of a meta server and press the Meta Server button, which will invoke the servers dialog where you can locate games over the Internet.
Using the Player Name field you can change the name that will be used to identify you to other players.
Press the OK button to connect to the game.
The servers dialog displays a list of Gnocatan games that are currently running on the Internet. When you select a game from the list, the host and port fields in the connect dialog will changed to point to that game.
You join a game by selecting it and pressing the OK button in the connect dialog. To obtain an updated list, you must close the dialog and re-open it from the connect dialog.
Recent meta servers also allow you to start new game servers on their host. If this is possible, the Create New Server button will be active and will bring you to the create server dialog.
In this dialog, you can select various parameters for the new game: board name (available types will be retrieved from the meta-server), default or random terrain, which sevens rule to apply, the number of players, victory points to reach, and how many AI players should join the game.
Once you're satisfied with your choices, press the Start Server button. The create server and servers dialogs will pop down, and server name and port will appear in the respective fields of the connect dialog. The new server will of course register to the meta server it was started from. You can see it in the list if you press Query Meta Server again.
The server started remotely will terminate itself automatically when the game is finished, or if sits around for more than 20 minutes without any connected players. Please also note that adding AI players will silently fail if the gnocatanai program is not installed on the meta server.