The Nook supports the open EPUB format for its e-books. This is a standard format that many publishers use to produce e-books. To manage digital rights on these files, many companies use Adobe Digital Editions software.
To download Ebook Central and EBSCO books from the MSU Libraries to the Nook, you must have Adobe Digital Editions (ADE) loaded on your PC or Mac computer. The download is a two-step process: first, you download your book to Adobe Digital Editions, and then you move the file into your Nook. To do this, simply connect your Nook to the computer with Adobe Digital Editions, and it will show up as a device in your library. Drag and drop the book you want into your Nook.
http://www.adobe.com/products/digitaleditions/ is the link to the free Adobe Digital Editions Software.
For e-books that can only be downloaded by chapter as a .pdf file, you can download them through ADE, or if you are using a Nook Tablet, you can download directly to your tablet. PDFs will be in the My Downloads part of the Library.