Back after the directions to shape the armholes (Front), the next section divides the work into left side and right side. Each of these will have a neckline side and a shoulder side. In the directions after the initial armhole bind off, when you divide for left and right sides:
Sizes S, M, L Only:
Next Row [RS]: BO 2[3, 2, -, -] sts, k to marker, work 12 sts in patt; sl next st to cable needle and hold to back of work, k next st, slip st from cable needle to left needle. Slip all sts from left needle to stitch holder. 51[59, 61, -, -] sts on needle.
You're to work across as the directions say and then slip the sts on the left needle to a holder. These sts are for the right side of the sweater. You're going to work the left side (as you would wear the sweater) first, then go to the held sts. The directions for the right side are further down in the pattern, before the Finishing instructions.