Aaaaaaaaaaaaaaah damn me I've understood !!!!!!
My oh my oh my !!!
Ok, here's why it's not my fault: In fact, I'd been adding "pages" all along and not "files" - Pages are what I'm working with in my French course.
As you say, to create a "file" we need to upload a little document such as a picture.
But as both icons are blue and rectangular with a folded corner, I was convinced I was clicking on the right one !!
Well at least that's that settled.
Thanks for your kind assistance.