I was a bit confused when the Nexus 7 failed to take my huge e-book collection into its e-book reader during my first attempt. The default e-book reader, Play Books, doesn’t take any e-book acquired outside Google Play. Below is my way to import my e-books collection in epub format, the application I used is Moon+ Reader which I found is highly customizable and has a very user-friendly interface.
Instructions of importing epub e-books to Moon+ Reader: