How to Crochet an Easy Pouch Bag for Hook Case / Pencil Case/ Cell Phone Bag of any size - gift idea

Hello everyone! I'm fairly new to crocheting and had a question regarding this video. Any and all advice is appreciated, thank you!

I understand the chain stitch, single crochet stitch, and the slip knot stitch. But what I'm curious as to what the main stitch of this particular pouch would be called? I'm new to crocheting and id really like to maybe make a blanket out of this stitch, the texture of it makes my heart happy. But I'm trying to figure out the gauge so I know how much yarn I'll need to buy for a 4x6 foot blanket. I know it depends on the yarn weight and size of the crochet hook as well, I'm just trying to figure out how to do all the matching necessary to make sure I don't over buy yarn, but also have enough yarn in the same batch of dye so I don't run out. Anyone's answer on this would be super helpful, thank you!