Not sure how to make it clearer, really. In the old days they called it "ankling", meaning that you used your ankles to try to maintain an even pressure on the pedals throughout the stroke. Thus the heel would be down before pushing through the top of the stroke, and up before the scraping motion you describe at the bottom.
A decent start is to try to get a feel for making a cicular motion rather than just stamping on the pedals on the downstroke. That's the best I can do, really, others may have more helpful imagery.