Hi and welcome!
You’re to work one shoulder first. Work in pattern across the number of sts for your size, for example, 17sts for the smallest size, dec by k2tog, k1 and turn. Leave the remaining sts on a holder or on the same needle but ignore them for now. You’ll get to them later.
P2 on the next row and work in pattern to the armhole edge.
Repeat until 11sts remain for size small and then cast off.
With the right side, or public side of the knitting facing you, rejoin a new strand of yarn to those held sts decrease by k1, sl 1, k1 psso and work in pattern to end.
Work in pattern to last 2sts, p2.
Repeat these 2 rows until 11sts remain for size small, work one more row and then cast off.
The decreases are all worked at the neck edge and the “p2” at the armhole edge.