I have a basic kindle. If I want to add a book, I plug it into the laptop and move the.book to the device.
My DM has a Kindle Fire and wants me to fill it with books. I am trying, but the device makes NO sense to me. I have dragged the books into 'Books' and only a third are showing on the device. Yet when I check thw folders of the KF on the laptop, all books are showing there 
Im going to end up.throwing it out of the window soon.