This is a more complete explanation:
http://projects.tynsoe.org/en/stm/doc.php
STM is just a nice GUI for the command line SSH. In fact STM will show you what command line arguments it is actually using, if you are interested. If you know how the command line works, you can open a tunnel from any computer (assuming SSH is installed as it is on all Macs) without installing any software.
Anyway, STM is installed on the machine you are connecting from (the client).
Name: What do you want to call this connection; can be whatever you want
Login: Your user name on the machine you are connecting to (the server)
Host: The domain name or the IP of the server
Port: The port to connect to on the server. Leave blank to use the default (which is 22 BTW)
Local redirections: This is where you define what local port you want redirected to the server. What port you need to redirect will depend on what you are trying to do: 1176 for the Indigo client and 8000 for Indigo control pages (assuming default ports). Just to keep it simple, keep the local redirected port the same as the port on the server (although doesn't have to be):
Port: 8000
LAN Host: same as the host address above
Port :8000
Remote redirections: not needed if Indigo is running on the same machine that is exposed to the internet. Useful though, see the docs for a complete explanation.
Port - Remote Hose - Port