How To Play Online Co-Op
Follow these simple steps;
Go to Custom Content from the main menu and click Share.
Find a map with Co-op in the name (i.e. “The Wrath of Felheim -2P Co-op” or “Commander’s Contest – 3P Co-op”) and download it.
Go to Multiplayer from the main menu and click Online.
Click New Match and then Host Game.
Click on the book next to 4P and then select the co-op map you downloaded.
Invite your friend to the match either through the Invite Friends button or by sharing the Invite Code.