How do I move photos from my Mac to Dropbox?

Drag your photo(s) to the Dropbox entry under Favorites then Drop them on the entry. Or you can click on the entry to open a Finder window onto your Dropbox. You can then drag photos from the Desktop into the Window. Or you can select the photos you want to put in Dropbox, then press COMMAND-C to "copy" them. Move over to the Dropbox window, click in the window to activate it, then press COMMAND-V to "paste" your selection in Dropbox.

If Dropbox is integrated into your Finder then it will be listed in the sidebar as Dropbox. Drag photos to it.