Could fill up pages on the process, but, for ease and future reference...and lest I forget, welcome to the FunFinder family and forum!
That rubber cap covers the E-Z Lube zerk. If you pull of the hub cover (the rubber cap inserts in the face of it), the hub removes just like a "regular" hub; you'll find a hub nut, etc.). Nothing "magical" or "different" on trailer brakes...the only difference is the magnetic puck used for actuation instead of a hydraulic slave cylinder. Operation and layout is the same as brake pad assemblies on a car.
Your running gear should be of Dexter manufacture and you can find a wealth of information (diagrams, parts #s, troubleshooting information, etc) on their website:
Dexter Axle and Brake Information
Anything and everything you would want to know about the Dexter axles and brakes!
You can peruse and download anything that you might need to keep your FunFinder "rolling along".