There’s minimal shaping of the armholes, just a cast off of 11sts for the second size. It’s the first direction after the Shape Armholes and Divide of Back Neck Opening.
The back neck opening is a slit at the back neck to make the neck easily slip over the head. You’ll divide at the back neck and work one side before the other.
“Cast off 11 sts, knit until there are 18sts on right-hand needle after casting off. turn and cast on 3 sts. (21) sts.” After you cast off 11sts there will be one stitch on the right hand needle leftover from the cast off. The pattern is accounting for that one stitch when it tells you to knit until there are 18sts on the right hand needle. When you turn, ignore the sts remaining unworked on the left hand needle. You’ll get to them later. You can leave them on the needle or put them on a holder.
Now cast on 3 new sts for a placket at the back opening. You can use a simple backward loop cast on here since it’s so few sts. Knit the 3 newly cast on sts and then purl to the end of the row on the 18sts.
This video shows the backward loop cast on worked before the turn but either way you want to add 3 new sts to the 18sts already on the needle.
Please delete the large portion of the pattern. We can’t post large portions of patterns due to designer copyright. What is the name and designer of the pattern please?