Hey Alex, I highly recommend watching this tutorial which shows how to setup a server with an IP address for connection, instead of sessions: How To Create A Multiplayer Game In 8 Minutes | Community tutorial. Basically this shows you how to setup a game with multiplayer for both LAN and WAN with an IP Address for connection. (So people from all over the world can join your server).
As for creating visible sessions for other players, you will need some form of system for this. It basically goes like this: when a session is created for the game, the subsystem also exposes that game. Without a system to do that, nobody will ever see it.
So you can create a basic system like this yourself if you have a website or a site to host your servers from. I know Microsoft Azure and AWS from Amazon is quite popular. If you go down this route just make sure that when a server is created save that server information on a website. The information saved should be number of players, type, public IP address, etc. Then when someone is searching for the server in your game, you simply load that website information and populate the game window.
Perhaps someone else knows of a system that allows you to host without a login, but as far as I know, there is no easy implementation.