I think you will be interested in the following two threads, both by our resident mechanical expert John Barca, and full of good close-up pictures to help with understanding.
The first one is all about maintaining your standard electric brakes and wheel bearings and is a sticky at the top of the Towing forum.
Annual brake inspection and Axle Re-Lube..
This one is all about Dexter Self Adjusting brakes and is similar to the 1st one but with different pictures and explanations of how the self adjusting brakes work. The adjusting wheel is under the magnet and behind the yellow spring at the bottom of the first picture.
Dexter Self Adjusting brakes.Both threads have good pictures of the adjusting star wheels down near the end of the opening post.
Hope this help you out! :)
Barney