Great, welcome to the online multiplayer community.
The most recent version of regular Sins is v1.18, I think, and for the Entrenchment expansion, it is v1.041. To update, you need to download and install Impulse, which is Stardock's version of Steam. Impulse is pretty benign and you don't need to keep it running to load or play the game, only for when you want to patch it. This is also the game's form of DRM, which is much nicer than having to put the CD in the drive or suffer from programs like CDkilla, Starforce, or Securom. (You can only patch it if you have a legit CD key.)
To play online, you click the <Ironclad Online> button and not the <Multiplayer> button, which is for LAN games. Most of the online action is for the Entrenchment expansion which is where you'll find the 4v4's and 5v5's.
