I've provided the links below to get you started on downloading on your Nook. Select the one that matches the device you own.
How to download to Nook e Readers
How to download to Nook tablets
Sarasota County Library System Adminstrative Offices: 1660 Ringling Blvd, Sarasota, FL 34236
Sarasota County Website | Sarasota County Library System Website