I don't know if I have just been lucky, but typically once I have taught a behavior I don't have to use the clicker anymore as a "good girl" can work in its place. When I do mini training sessions at home, I do try to use the clicker as I think it is the fastest way to shape new behaviors.
I think maybe you should just start over training Denzel from scratch, but I am sure he will be very quick to pick up the behaviors you have previously taught him.
When in college, before I had my girls, I had a bullmastiff that I clicker trained. He was the family dog that didn't come to live with me until about age 5, but I managed to teach him quite a few things.
Here are some videos of me using the clicker with him:
I, too, had a hard time understanding what behaviors were being rewarded in the video with Izzy. I should say I was a psychology major, and one of the things I did in my Behaviorism class was train animals at the zoo using positive reinforcement/clickers.
I think it does help to have a basic understanding of how clicker training works before you start. Don't Shoot the Dog by Karen Pryor is an easy read that I think does a pretty good job of explaining things.