Networking
Once in a lobby, the networking is built on top of Steamworks Networking Messages. While you can make your own custom networking, it can be quite complex. Luckily, there are many great networking frameworks for Unity which MPE4S supports:
For most users, using an integration with a networking framework over a custom networking solution will work perfectly for their game. Integrations were created for these networking libraries as they are all great options, so if you are unsure on which to use, we recommended reading an overview of each to see which one sounds best for you and your game.
MPE4S is designed to utilize the free lobbies and relay systems which Steam provides, meaning it uses a peer-to-peer networking model and does not support dedicated servers. However, you can still implement a classic client-server model by designating the owner as the host or server, and allowing them to maintain authority over the game. This is exactly what the networking library integrations do.
Testing
To test your game's multiplayer functionality locally, check out the testing documentation.