When you add books to Calibre, they will usually be added to a folder on your computer (Calibre Library). If the book you want to put on our husband's Nook is already in the Calibre Library folder on your computer, connect his Nook, open Calibre, click on the book and use "Send to device" option.
If it is on your Nook, but not on your computer, first connect your Nook, open Calibre and add the book to its library from your Nook. Disconnect yours, connect our husband's and "Send to device".
I find Calibre to be user friendly at times and a bit of a "head scratcher" at other times.
I used to use Caliber's "Send to Device" button** . . . but now I simply have the Calibre library open in one window and have another window open that shows my NC "Books" folder.
I then Click and Drag the book title right from the Calibre window and Drop it into the Books folder in the other window.
Calibre can be as simple as that!
I hope that helped.
**I don't anymore because I'm often trying to put a Kindle book on my rooted NC. When I use the Send to Device button, I guess Calibre sees my device and thinks it has to perform a conversion on the Kindle .mobi file. I haven't bothered to figure it out because Dragging and Dropping is so easy.
I posted this on the General forum but got no response. Maybe someone on this forum can provide help. My "oldsheimer" has kicked in--or I am going brain dead. I have successfully transferred a couple of books from my NC to my husband's NC several weeks ago using Calibre but now I can't remember how I did it. Could someone please give me step by step instructions how to get a book off my NC to my husband's? I have been trying for hours but all I am now getting is multiples of my books in MY Library on my NC (ugly grey covers). Also how do I get the multiples off my NC? I will be very appreciative. (Note--I am very computer illeterate.)
The calibre forum on mobileread.com will answer your questions.