on 07-24-2013 07:19 AM
FYI, it's supposed to look like an "N" for Nook, not a "U" (for upside down.)
Try using the QuickDrawer on the bottom right hand corner (looks like two boxes.) If you're in a book, you might have to tap the notification area first to get the boxes to pop up. If they arent showing up as an option, go to Settings →Applications →Home → Select Recent Drawer option at the top. You won't be "exiting" the apps, but quickly moving between them.
To "exit" apps, some will allow you to exit by selecting the back arrow on the bottom left. For others, you need to find the exit in the app settings. Depends on the app.
See if either of those ideas works for you.