To download an entire book for reading offline, you will need to install Adobe Digital Editions on your computer and to create an Adobe account.
Create an Adobe account:
The above step-by-step instructions provided by the ebrary Knowledge Base.
Download a book to your computer:
You must have Adobe Digital Editions installed on your computer. See the instructions on the left hand side of this screen.
Connect your Nook to your computer with a USB cable.
Launch Adobe Digital Editions. You may be prompted to create an Adobe ID. See the instructions on the left hand side of this screen.
Adobe Digital Editions will automatically detect the Nook and may offer to authorize it with your Adobe ID.
The Nook will now appear as a new bookshelf in the library. You may need to click the library icon in the upper left hand corner to get to Library View.
Click on the downloaded book and drag and drop it to the Nook bookshelf.
By clicking on the Nook, you will see all of the items on your Nook device.
Although your downloaded books will expire automatically at the end of the loan period (generally 14 days), you may return books early:
In Adobe Digital Editions, click the arrow on the title you wish to return.
Select Return Borrowed Item, then click Return.
You may need to return the book from the All Books bookshelf to remove it from your computer also.