In one sentence, describe what the following article is about:

This will reveal a dialog allowing for the changing of the wallpaper as well as the cleaning of the home screen. This will bring up a dialog allowing you to choose your new wallpaper. Take note of the tab labeled "Photo Gallery", as this contains more photos that may be set as the wallpaper. This may not be necessary for the photos under the "Wallpaper" tab as they are optimized for the screen size. Take note of your ability to pinch and stretch your fingers apart to re-size the frame that represents your screen.

Summary:
Tap and hold down your finger on the Nook home screen. Tap on the option that reads "Change Wallpaper". Tap on the wallpaper that you wish to set as the home screen wallpaper. If necessary, re-size the picture. Allow the wallpaper to finish loading and return to the home screen.