Basically, the “default” multiplayer setup from unreal engine is “Listen Server”.
Listen server mean a player will host the game.
You can also add dedicaced server but it can be only on a source compiled engine.
To match player together, you will need something to do the link between players,
You can go on a custom solution, or use online plateforme like steam, epic online service…
Everything is free, and implemented directly in unreal,
Some plugin on the marketplace will do the task easily.
To learn how to do multiplayer games with ue4 : Official doc is a good start place,
But there is MANY good tutorial to improve your general understanding of the flow on Youtube (free) or Udemy (notfree). You have also the An Unreal Engine Blog – An Unreal Engine Blog.