This little sweater is knit from the neck down. So the garter stitch ridges are the neckband. To get two ridges you knit 4 rows. The rule is two rows make a ridge.
Work even in garter st (knit each row) until 2 purl ridges on right side.
(RS) Button hole - k2, YO, k2tog, k across.
If you cast on and then your first row is the right side, you would knit that first row, then two more and you will be back to the right side facing for the next row which they give as the "RS Button hole" row in those instructions above.
The body of the sweater is in stockinette, and the edges are garter (knit every row).