You can add pics to your NC by connecting it to your PC and simply dragging files from your PC to the Pictures folder on the NC. Or you can copy and paste them any other way you would normally copy and paste files on a PC. The NC looks just like another hard drive (or two if you have an SD card installed) to your PC.
How do I actually download pics onto my nook color? Please help!
The User Guide has the answer to most questions posed her by new users. There is even a copy on your NC.
The section on file management begins at the bottom of page 48:
"Transferring Files from Your Personal Computer to Your NOOKcolor"