To use a script, you need to use the listen command to open a port for a script.
You pass this command a third argument which states which script to use.
See tcl-commands.doc for further information on it.
As for making a DCC session (by the way, it is a DCC chat), you do need a CTCP command. The format is
\001DCC CHAT chat <formatted_IP> <port>\001
You replace the two items in <> with two seperate values.
For port, you use the port specified in the listen command.
For the formmated_IP, use the return value of the "myip" command.
It is a IP converted into a integer, the same as that used in the script I posted to test if a IP was from a private LAN.