It's not a dumb question, we are all trying to learn together. I have a Windows Vista computer so I don't know if this changes with a Mac.
The only thing I use Adobe Digital Editions for is adding books (EPub's or PDF books) onto my NC. If you want to add other things like pictures, wallpapers, etc... just use your Nook USB cord and plug your Nook into your computer. When you turn your Nook on you should have a new window pop-up showing your NC is connected and asking what you want to do. I choose the option Open Folder and View Files. You should see a Folder called My Files. Open that and you can see where you would add pictures and wallpapers. You can just open the file on your computer where your pictures, PDF's etc... are stored and either copy and paste into the correct Nook folder or drag and drop the file.
I also add PDF's that are in the form of Newletters with lots of articles and pictures. I just directly copy those into the Documents folder on my Nook.
If you have something that would look better if it was converted into a different format (like an unprotected PDF to and EPub) I use a free program called Calibre.
Once it is converted you will be able to add to your Nook when you hook your Nook to the computer with Calibre open. You should see an option at the top of Calibre to Send to Device.
Make sure to close Calibre and then safely remove the Nook from your computer. Don't just unplug it.
To find it on your Nook, go into Library then My Files then either Books, Pictures or Documents etc. You can also go into My Shelves and click on Edit. You should be able to see any PDF's or books and add them to a shelf to find then easier.