(This question is for Gamers that play Garry's Mod on Steam) How do you make a Garry's Mod server?
To make an online server, all you have to do is select create multiplayer option, on the main menu. Then ensure that you uncheck the LAN checkbox before you start the game. This will make your machine to act as an online server, which can be joined by other players. See http://www.wegame.com/games/gmod/how-to-make-an-online-garrys-mod-server/.