Let me see if I can explain the hand stitching method without pictuures.

First you would fold Pleat A, figure the taper, then fold Pleat B, figure in its taper. The material for Pleat C is folded back, not out in front. So all you have in front of you are Pleats A & B. Next you would sew the edge of Pleat A to Pleat B.

Then you bring up the material for Pleat C. Fold it with it taper and pull the rest back, not forward. Then sew the edge of Pleat B to Pleat C.

Keep repeating until you have all the pleats sewn.

Clear as mud.