The first stage is to look up the manual as reference

http://manual.3dgamestudio.net/

under network functions.

This gives you an overview about what functions are
relevant for multiplayer, and how they basically work.

Some small recent games of mine:
Griefer 4k http://damocles11.byethost9.com/griefer4k.html
Kobold 4k http://damocles11.byethost9.com/kobold.html
Cave 4k http://damocles11.byethost9.com/cave4k.html