Barnes & Noble has its own e-reading device, called the Nook, and its successor, the NookColor.  Their self-publishing platform is called "NookPress" replacing their previous portal, "PubIt!"  It's a shame that they renamed it--at least "PubIt" made the type of file you're supposed to upload there easy to remember because Barnes & Noble, with whatever name they choose this week, takes ePUB-formatted files.  Not MOBIs, like Amazon; ePUB.  (If you need a refresher course, revisit our article What Are the Main eBook Formats? While some people use the term "ePUB" to mean an "eBook," much as "Kleenex" has come to mean "tissue," ePUB is actually a specific ebook format.  It's now one of the two primary eBook formats, the other being MOBI (Amazon Kindle).  

The Barnes & Noble Publishing Portal:

Barnes & Noble's portal is located here:  NookPress and once you've uploaded a book to Amazon, uploading to PubIt! is remarkably similar.  Once nice thing about Barnes & Noble's platform, compared to Kindle's, is that you may upload up to five (5) reviews or blurbs your book has received, in addition to the description of your book--so make sure you have those handy when you get ready to upload.*

You'll also need your cover image readily-accessible, and to make sure it's NookPress-friendly, make certain that it's not less than 1000px wide on the short side, in jpg format.

* One not-so-nice thing about B&N's portal is this:  if you have a professionally-made ePUB, or an ePUB that you've made yourself, whatever you do, don't edit it in the NookPress publishing portal, where they allow you to make changes. Why?  Because if you do, B&N inserts what's called a "stylesheet" (CSS, in the business) that overrides the one that you or your eBook Conversion company made for you, specifically for your book.  This overriding stylesheet may significantly alter the look and even the functionality of your book.  So:  don't edit, or make any changes, while in the NookPress portal.  You've been warned!