I have a feeling the game will come to you all updated to the latest version, not entirely sure, someone correct me if I'm wrong.
If not at shipsim.com there is a page called "Patches", you can download the latest update there which includes multiplayer.
Providing it is all set up properly, there will be an option on the main menu called multiplayer.
There are various companies, go to Small Talk and look at the topic in bold at the top of the page. Come To Our Fansites and Community Forums. Take a look in there, lots to choose from.