This site is being deprecated.
Please see the official X‑Plane Support page for help.
In general, networking in X-Plane works only if you are both on the same network. That could mean the same wifi network if you're able to visit each other at home, or you may need to connect via a third party such as VATSIM. Multiplayer servers is not a service X-Plane provides at this time.
This forum may have some good archives to help you get started, especially this thread.
This site is no longer being actively maintained.