To use a Nook eReader or a Nook Color with Freading you'll need a computer with Adobe Digital Editions installed and authorized with an Adobe ID.
With Digital Editions opened on the computer, connect the Nook to the computer with the USB cable that came with the Nook. Once connected, Digital Editions will recognize the device and ask if you would like to authorize the Nook with the same Adobe ID as the computer. Select "Yes", and you will see the Nook appear as a bookshelf in Digital Editions.
Now, when you download a book from Freading and open it into Digital Editions you will be able to drag it onto the Nook.