How to Work the Gathered Stitches of Hills & Hollows

The first video below shows how to work RLI, LLI and the decreases on the RS (knit side).

The second video shows how to work RLIp, LLIp and the decreases on the WS (purl side).

How to work RLI, LLI, ssk and k2tog
How to work RLIp, LLIp, p2togtbl and p2tog