Help converting to .epub and reading on Nook app

[RandomNumber]

I'm a new user to the Nexus 7 and am getting very frustrated. I want to take books I buy through Amazon and the Kindle app and read them with the Nook reader in my nook library. I figured getting them their was as easy as downloading Calibre and copy/pasting. Apparently not. I managed to find a .DRM cracker plugin for Calibre and was able to convert my wanted book to .epub, but have no idea idea what to do from here. I put it on the device with Calibre and now need to somehow get it into my Nook library. How do I do this? Please help a new user out, I'm ready to just send it back for a Kindle Fire.