With regard loading your books on to the app. Your Kobo books purchased through Kobo should appear automatically (when you first load the app it syncs with the server). For locally stored epub books I created a folder and copied them there from my pc. Then in the Kobo app in library view at the top right there is a vertical line of three squares. Click on this and there should be two options, import content and settings. Clicking on import content will initiate a search of your files to find any epubs which you can then import to your library. This works in exactly the same way as it did on the Kobo Vox. In fact I found it worked better as it found epub files that the Vox couldn't and others are readable now which for some reason they weren't on the VOx. This is how it worked for me on the Galaxy Tab, I am sure the app works the same way on the Nexus.
Hope this helps!