This pattern uses the fisherman's rib stitch pattern, which requires you to knit and/or purl into the stitch below. I was asked a few weeks ago about how to knit this particular stitch. I thought I'd post this video tutorial that I found on YouTube which does a great job of showing how to work this stitch pattern.
How to Knit the Knit One Below Stitch (K1B) by newstitchaday
The Purl Bee, one of my favorite knitting websites, also has a photo tutorial of how to work this particular stitch, with two accompanying patterns for a scarf and cowl here. Enjoy and stay warm!!
PS:If you aren't a knitter, I have these chunky, ultra-warm infinity scarves for sale in my Etsy shop!