That is provisional cast on. It is made with a crochet hook. There are 2 versions that I know of. The first, you crochet a chain in contrasting yarn, then knit into the purl like bumps in the chain. The second, you crochet live stitches directly onto the needle. With either method, you remove the base of contrasting yarn later. And you pickup the stitches & work in the opposite direction.
You should be able to goggle videos of both.