Need a bit of help on a new game in devolopment


I am making a online fps game. The game has all the guns and animations ready, but I cant seem to find a place where I can learn how to make a “global” multiplayer (a multiplayer that doesnt just work when you are on the same wifi). If any of you have any tutorials on this please leave a link to it or if you know what to do please tell me.

Does anybody know where to get sci-fi lokking assets and ships?

Thanks if you answered or just joined!
If anyone wants to we can maybe have a discussion about this down below in the comment section

EDIT: (sorry for potensial bad English)