B-skips are a little more fancy than your basic A-skip. The first motion is the same. Drive the knee upward the same as you would with the first exercise. Instead of snapping it back down though, extend the leg and bring it back down striking the ground below with the forefoot and kicking back until it’s aligned with the hip. When doing the B-skip, it should feel like the leg is moving in a circular motion.
See video here.