If you're knitting in the round and doing stockinette you don't need to purl. There are no purls in the scarf or the sample at the tutorial. The scarf and the sample are knitted on the outside of the tube. I'm not sure what you're seeing as purls.. You will only be knitting if you're knitting the scarf as a tube, in the round.
Are you talking about the way she's knitting? She's showing you how to carry the yarn across longer spans so you don't have long floats..is that what you're seeing?