It's fairly straight forward and will vary slightly depending on what year we are talking about...... At the firewall bulkhead for the wiring harness, you'll find a large (8-10 gauge) red wire w/ a white tracer stripe that goes down towards the OEM igintion module (it's the small box mounted on the fender well below the steering column). You're going to cut it before the module, splice into it and run a new wire the "Batt" terminal of the DUI. Your DUI or any of the GM style HEI's are reffered to as "single wire" connections because you only have a single hot wire running to the cap. If for some reason you can't find the "Red" igintion control wire for the module (like if the harness has been hacked up or you have a "points" ignition), you can re-wire/splice into a circuit that is "key on/start". I have seen some guys use the starter relay (the "I" post) for this too- not a big fan of this route. But eitherway will be based on the existing distrubtor setup.
Personally, I like to remove all the factory DuraSpark (or points if its an older motor) components/wires during the install. But if you're not completely comfrontable with the install, you can leave them disconnected and in place until you're confident everything works.
FYI.... the other terminal on the cap is marked "Tach" which is for your tachometer. If you have the factory/OEM tach, you may have some difficultly setting it up. If that is the case, let me know and I'll help you with that too.
Keep me posted Bro...
John