Not too much to add to the very useful advice from GenkiGenga and ranma - do a search on 'mulitplayer' and you'll find lots of interesting and informative discussion (here's one example); the server-side coding is critical, since the actions of your players have to be communicated by the server component of the game (which is not Construct 2's job).
My own advice: think about making multiplayer games only if a) you've got lots of experience in networking and server-side coding, and b) you've got lots of time on your hands.