@grizeldi It takes time and patience. When I first started I had no clue what was happening with nearly the whole engine. Now , I've spent time learning and mastering it I'm starting to put out stuff that looks like professional quality games.
I've been working with JME for about 2 years now I think. It has taken me at least that long to grasp the fundamentals and master them. You're only going to get out of it what you put in.
You should visit some shader sites and learn the core of what makes them tick. Don't be intimidated by the math. There are people out there who make shaders and do most of the math for you. You just need to learn what variables to change and when.
@MoffKalast I would assume a minimal standard level of intelligence among anyone interested in programming a video game. Anyone who lacks that basic degree of intelligence won't last long , maybe a month or two.