Now that we've learned the specifics of replication and the default classes that are available to us, we can see how important it is to design with multiplayer in mind from the start rather than trying to implement it later. Even our simple Awesome Game pickups and weapon equipping needed significant changes to work in multiplayer. It's important to test frequently on both the server and client to make sure your code is functioning properly.
By default, the Unreal Engine is able to use Steam for multiplayer, but setting it up and connecting through your friends list requires a bit of extra setup. The documentation for a Steam setup is here: https://docs.unrealengine.com/en-US/Programming/Online/Steam.
And to connect to a multiplayer game through your Friends list, along with a host of other session functionality, I highly recommend Morden Tral's amazing...