There is no replacement for hands-on experience. If you want to better understand digital accessibility, get your hands dirty. Try out a screen reader. Give keyboard navigation a shot. Dig into the code if you're able. If you don't typically experience accessibility issues yourself, or even if you do, in the field of accessibility you generally learn by doing.
First, we do need to ask that you keep in mind:
Have you ever taken on a small home repair or improvement project and been surprised by the issues that came up? You watched all of the do-it-yourself shows and videos online and it looked so easy. Measure this, cut that, slap on some paint and ta-da — the home of your dreams.
First, the content you watched that gave you the courage to do it yourself probably looked easy because experts were doing the work. Years of practice can make things seem effortless, but not seen are the countless mistakes and lessons learned to get to that point.
Those lessons learned can't be discounted, though. They are everything.
You can read every book and watch every video on whatever it is you hope to do. When you pick up the tools and start doing it yourself, only then are you going to really understand what that content was all about.
Most likely, the job will seem much harder than you thought at first. As you keep going and get the hang of it, things start to get easier — or, you at least understand them more. "Oh, I want to hire a professional for this, or, "Wow, I really can do this myself," are realizations you might not come to until you learn what's involved. That comes from doing.
Want to get your hands dirty? Here are some resources: