How to make multiplayer

I’ve wondering how to make a multiplayer game that works online and offline/local wifi[hotspot].
With the game discoverable in the game.
If it has javascript or not i still need to know.

If its really hard to do it maybe if there’s an extension that makes it easy to make multiplayer.

Thx ^-^

arthuros P2P extension is native to GD now, no need to download it.