You have probably imported the photos using the COPY option, and so Lightroom places a copy in some other folder, and uses that copy in that other folder. It does not know about the original photo in the folder you think it is in.
If you have no (or little) editing and adding of metadata to these photos, you could just start over with a new catalog (File->New Catalog) and import using ADD. Then the photos will appear in Lightroom in the folder you think it is in, and no copies will be made.
If you have done significant editing and/or adding of metadata, starting over would cause you to lose your edits and user-supplied metadata. But there's really no easy way to continue and fix the folder problem without a lot of further discussion, which also would involve providing screen captures.
Please consider viewing or reading some introductory tutorials on Lightroom, for example:
I do not have any photos that have been processed that I need to keep yet. Still working thru all the set up and a lot of learning about what to do when I do start to edit. If I can clean up this mess, maybe its a good idea to start over with a new catalog. If I do create a new catalog. How will I tell it from the old one? Should I and how do I delete the old catalog so as to not be confused. I can fix this now before I get a lot of edited photos.
I have laid out all of my original photos in a folder on my desktop and I won't be adding photos to lightroom from a camera card. They will always be
imported from the desktop portfolio folder...So, I should always use Import ADD instead of copy?
You would use ADD as long as it meets your needs. And you would use COPY or MOVE if one of those meet your needs.
Should I and how do I delete the old catalog so as to not be confused.
You give the new catalog a new name (it asks for the name when you select File->New Catalog) and then you can use your operating system to delete the old catalog file, the name ends with .LRCAT (you can tell it is older by the date the file was modified).