I'm making an MMO, how do I persist user data, position, etc?

Hi, so far I’ve read people use Steam Multiplayer or that kind of solutions, but I want to own my data and my server.

I haven’t been able to find any “right way” to have a server and store data, player position, movement, etc. Do I need to have a “standalone” client running and have the other players connect to its IP? Then how do I persist data?

yes, you want a dedicated server to run and host the game (google for UE dedicated server - there are good tutoarial in the wiki and on youtube). where you save your settings depends on your setup - a dadabase or api server would be a good idea, if you have a dedicated or root virtual server you can also use sqlite or a simple savegame file