How do I hook up a server to my game?

I want to get a server which keeps track of all connected clients, and sends messages to clients so that they can show what's going on. Firstly, how would I do this? Would I make a unity program which opens up a server, and make a client one that connects to that, or can I have the server up WITHOUT starting it in unity? Secondly, what commands are there that "request" from a server? How do I actually connect a client to a server? Is there an already-answered question for this? Or a big tutorial for all things MMO? I'm sorry if all these have been asked before, I haven't been able to find anything yet. Am I just bad at google? :P

Links to other answers are okay, I haven't found one that answers my question properly yet, which is why I'm asking.