I've read a post that by deleting folders I also delete photos from the disk and catalog. I want to delete all my photos, save those same photos, which are on a memory card, to an external hard drive and import the photos again. Most of the 500 or so photos are missing files. May I just forget about trying to fix the files and just delete all my photo folders? I'm using a MacBook Pro.
If you delete the folders from your Finder, the photos are deleted from disk but the catalog is not updated and all your files stay in the catalog as 'missing' files: the links to their original location is broken. You simply have to delete the catalog and create a new one if you decide to import the files again.
If you delete the folders from the organizer, you are right, the photo files are deleted and the catalog is updated (it becomes empty).
If you decide to re-import from 'camera or card reader', you decide where you want your files to be copied from the card. I would create a new master folder like 'My Photos' on your drive for that.
I would only delete the original folders and catalog on your drive after reimporting in the new master folder to follow the good practices you were given about backups: test if the new import works as expected, better still, do a backup from the organizer on an external drive. Then you can get rid of the original folders. Personally, I don't delete the files from my cards unless I have downloaded and backed up them twice.