Discretion Module Tutorial
From ASSS Wiki
This tutorial is divided into a few pieces. If you're completely new to Discretion development, you can view them in order, otherwise you can skip to the one you're interested in. If you go in order, they assume you have no knowledge and no tools installed.
Obtaining the Discretion Source using Subversion
Creating and Testing a Simple Discretion Module
Discretion Commands and Displaying Images (Also covers listening for callbacks and using interfaces)
Listening for Key Presses, Displaying Text, and Per Player Data