The Barnes and Noble Nook App is not available in the Amazon App store. It is, however, possible to download the nook app to the Kindle Fire by going outside of Amazon’s authorized app store. While the process is not difficult, neither Amazon, OverDrive, or Barnes and Noble will provide support for the Nook app on a Kindle Fire. Amazon will not support problems caused by downloading non authorized apps. The library is offering this for informational purposes and assumes no responsibility for any issues arising from downloading non authorized apps. Please proceed at your own risk.
In short, here are the basic instructions for downloading non amazon apps to the Kindle Fire The process may vary slightly in different versions of the Kindle Fire, Fire HD, and Fire HDX.
On the Kindle Fire go to Settings (swipe down from the top to get to the menu, and select Settings)
First listing is "Apps from Unknown Sources - change to ON. This will allow you to add apps that are not in the Amazon app store. You will see a warning message:
When you use applications from unknown sources, your Fire and personal data are less secure and there is a risk of unexpected behavior. You agree that you are solely responsible for any damage to your Fire or loss of data that may result from using these applications.
This site has a video and screen shots of how to install 1 mobile market on your Kindle fire. http://kindlefireforkid.com/how-to-sideload-android-apps-in-kindle-fire-kindle-fire-hd-and-kindle-fire-hdx/