Moving photos from finder to photos

You can just drag folders of pictures to the Photos icon. You'll be asked if you want to "Keep Folder Organization"-- you'll probably want to say, "Yes." Leave "None" for the album name. You may end up with some extra folders, but it works well. "Import All New Photos" checks to see if you are trying to import pictures that are already in Photos.

Your folders of pictures will still remain in the Finder, so they provide a backup. You can delete them once you're convinced Photos is doing what you want. But you may, instead, want to move the Finder folders to an external drive, or even a flash drive, for a longer lasting backup.