The best way is to read the Amigaguide manual downloadable when you join the OctaMED Yahoo Group. Then load up OctaMED and a MOD, and let it play. Try to figure out what's going on by watching and editing the code inside the MOD (the AmigaGuide manual will give you a clue as to what the codes do).
You need to understand the basics of music construction in beats/bars/measures though first....otherwise it might not make much sense and you.