Oooooooooooohhhhh! I *think* I get it now. I've literally never used the "History" function up until now. I still can't quite understand how (in your screenshot/animated examples) the flat surface full of points is generated beneath the extruded shape. I can see a flat load of points when I select/add points to a flat shape, but they don't form a solid flat sheet/object like in your example and I'm not sure how to make it so. Is there something I'm missing?

Thank you very much for taking the time to show/explain it nonetheless, pal. :)