1. "Multiplayer" is used for LAN games only.
2. "IronClad Online" is where you create your "online player" (add player......after loggin in) and create, join games.
If you're on game version 1.05 (game-versions are shown at the bottom right when in-game at the menu) you'll need to download my guide "Networking and SINS" (for port-forwarding information) which can be found here , linked-to right under the GREEN writing.
If you've used IMPULSE (www.impulsedriven.com which is required to get patched to anything past v1.05) and patched your game to the latest BETA version (v1.095) you won't need to follow the steps in my guide as the new netcode (ALLOY) tunnels past routers etc. with ease. To find the BETA in Impulse you need to click the blue ORB in the upper-left corner and make sure "pre-release" versions are being shown.
thanks,
the Monk