shape armholes

what does this mean? I am doing a knitted sweater

Shape the armholes.
Cast off at 6 sts at beg of next two rows

Next row k2, s1, k1 psso,to last 4 sts, k2tog k2.

Welcome to KH!
Bind off 6sts at the beginning of the row, work to the end of the row, turn and bind off 6sts at the beginning of this row. Work to the end of the row. On the next row you’re to decrease 2sts in from the ends. Knit 2, slip one as if to knit, knit 1, pass slipped stitch over the knit stitch. Work to 4sts before the end, knit 2 together, knit 2.