Click the ironclad online button from the main menu.  There is no automatic matchmaking really.  You will make a name and be taken to the lobby where you can join games or host your own.  The busiest times are in the evening Eastern US time.  Most games are played with entrenchment although you may find some regular sins games out there.

[_]-Greyfox

Unfortunately the buttons are misnamed.  The "Multiplayer" button is for LAN games.  The "Ironclad Online" button is the one you want for online multiplayer.  To play online you need to have the lastest patched up version of the game.  (You patch it with Impulse at http://www.ImpulseDriven.com.  You have to create an account and register your CD key, etc.)  When you click Ironclad Online you'll also need to register an account and then create a player name ("Add Player") and then select it ("Use Player").

Anyway, welcome to the online multiplayer community!  Sins online is much more challenging than playing against the AI and it's a tremendous amount of fun once you know what you are doing and can hold your own against the other players.

NO! Stay on multiplayer! please!  But damn, that does sound like a ruff start of it hahaha