Creating Multiplayer Games
You can create a Online Game Session using the “Create SteamCore Session” node, if the creation is successfull you open your map with the “listen” options so that it will listen for multiplayer connections
This Example has a Video Tutorial that you can find here: Related Video
Creating the Session
To create a simple Session all you have to do is call the "Create SteamCore Session" node and then open the desired multiplayer level with the "listen" parameter so it will accept multiplayer connections.