Welcome to the forum!
The sweater looks lovely, very neat and even knitting.
The part of the pattern you highlighted has you knit to the end of the shoulder sts then k2tog. Call that row, row 1.
Decrease at the armhole on rows 3,5,7,9,11, 13 and 15.
Decrease at the neck edge on rows 2,3, 5,7,9 and 13.