This technique looks confusing, but is not difficult to sew. These alternating pleats are just created by marking pleats at the top, and the bottom. The pleats at the bottom should be marked directly in between the marked top pleats. When you sew the pleats, it looks like the fabric is folded in on itself and intertwined together.
Slash-and-stitch-and-stitch, without much fraying: Helen Jones class sample. "Fabric manipulation techniques are used to change the appearance and texture of cloth to create a new surface which can be an end in itself or can be further embellished. These techniques include pleating, wrinkling and scrunching, twin needle work and collage."