Step by step of what you need to do.
1. Have All Players set their name to the same name they used in the game you played.
2. For a Host to load a game in multiplayer (only One Player does this).
a (LAN and IP) From the main menu go to Multiplayer then (blue) Load Game, select the game and press the (green) Load Game.
b. (IronClad Online) After logging in have the host go to (arrow pointing up) Host Saved Game, select the game you wish to load then press (play button) Host Saved Game.
3. Now that the game is hosted All other players now join the game.
a. (LAN and IP) In the main menu go to Multiplayer then Join Game, enter in the IP if playing by IP or select the game if playing over Lan, then press Connect.
b. (IronClad Online) After logging in go to (blue) Join Game select the game you wish to join then press (green) Join Game.
4. When all players have arrived (you can tell if they're there by the ready button) have all players ready up and then the Host presses Start.