This is another area where Ironclad screwed up. Instead of Multiplayer it should be called LAN games with Ironclad Online being called Multiplayer.
The button that you want is the Ironclad Online button. You then need to register an account with ICO and make a player name. Then you can join the ICO lobby and you'll be able to <Join Games> and see the games that are available. Welcome to the online multiplayer community.
