The help is all in the extensive helpsystem:
perform checklist for net connections
This finds all types of net connection you have that are supported by DirectPlay.
for x = 1 to checklist quantity()
if lower$(left$(checklist string$(x),3)) = "int"
Internet = x
endif
next x
finds the Internet TCP/IP connection value(if avilable)
set net connection Internet,"255.255.255.255"
sets the connection to be internet TCP/IP for a client - if you have a static address for the server, use that instead 255.255.255.255 - that searches every IP out there
set net connection Internet,"127.0.0.1"
sets the connetion to be internet TCP/IP for a server - only games on your 1st loopback IP can be detected, since a server won't be joining sessions, all it does is save time by not searching every IP.
perform checklist for net sessions
displays a list of all net games written in dark BASIC that are currently running (you will need to make a filter of your own (like the way I find only the TCP connection) to make it show only the server(s) for your game.
Just assuming your game is net game number 1:
join net game 1,PlayerName$
this joins the game and calls the player on current machine the contents of PlayerName$ (so save this string before you get here obviously)
after that, who knows what you wants your clients to do...
now, for setting up the host, the connection is already set up for TCP/IP
create net game "My MMORPG Server",ServerName$,255,2
this creates a net game called My MMORPG Server, with a maximum of 254 clients allowed to join (you have to count yourself in your game), and the server's player name is the contents of ServerName$ - it's silly giving it a proper player name since the MMORPG servers are usually dedicated, so there won't actually be a player there manning the computer, but still it must have a player name.
THIS CAN NOT BE ACHIEVED FOR ANY SYSTEM THAT IS BEHIND A NAT (SUCH AS A ROUTER - THIS IS IN CAPS AND UNDERLINED BECAUSE IT CAN NEVER BE STRESSED ENOUGH)
If you're getting stuck and lost at this stage, before the game is even started, can I suggest an offline adaptation of your game first?