The current version of Construct 2 doesn't officially support multi-player at all, other than providing the very basic facilities offered by the AJAX
plug-ins. These provide some basic functionality for establishing connections and sending/retrieving data, but nothing higher level and obviously nothing server-side. They would be sufficient for most turn-based games, but in the general case won't be suitable for more real-time multi-player games, and you'll have to handle all higher-level logic (such as synchronisation) for yourself. This may be further addressed in future releases, as multi-player functionality is a pretty popular request.
That leaves you with third party plugins
anything you can find in the forums. I've seen some good progress from some users, but don't have any links handy or specific advice on it -- other users might have more information for you.
Hope that's helpful.