In my opinion, you're having a little "culture shock" after moving from the Windows environment. Just keep this in mind: Android and other touchscreen devices are designed to be
easy. In fact, the goal is actually to eliminate much of the hassle of Windows. The idea is that you shouldn't have to copy around files. You shouldn't have to worry about messing up your tablet's settings. In fact, I rarely open my file explorer. Most of the time, I just trust that the various Android applications are going to store my information in the right place.
Unfortunately, due to the fact that the eDGe is now a retired product, you will have to use the file explorer to copy around digital books and *.pdf files. But it's not that difficult. I like the Google eBookstore, and you should be able to find instructions on how to easily download and copy over books into your library.
So my advice is just to take it easy!
You'll figure it out!