I am having a hard time understanding this instruction:(I have 56 stitches on my needles)
Cast on 12 sts at beg of next 6 rows. That will give me 128 stitches.
Do I cast on the purlside too? I have the arm knit, these stitches are for the body.
Yes, cast on at the beginning of each of the next 6 rows. Use the knit CO, but it won't matter if it's a knit or purl row, the CO will be hidden when you seam up the sides of the sweater.