Where do I find any documentation on how to send and recieve packets from/to a websocket server
Websockets are coming in Godot 3.1 (I think). You can look at Faless’ repo, which has a multiplayer example. I do not think there is currently any documentation for websockets, though that will likely change once Godot 3.1 is out.
Is it possible to run a game with an external parameter like a GET or a POST value?
I’m not sure. I don’t think it’s possible, but I know little about web programming.