"Lap the top garter stitch (every row knit) border of back over front and stitch through both thickness for approx 2 3/4" from each end for shoulders."
This will make a boat neck for the sweater. Lay the front out on a table with the outside (or public side) facing you. Place the back on the table so that the two pieces meet at the shoulders. Overlap the back garter stitch border over the front and sew it to the front for 2.75" on the left side and then repeat on the right side. The look of this type of shoulder may show up in the picture of the pattern.
"Place markers 6 1/4" down from shoulder seam at side edges of front and back. Sew in cast off edges of sleeves between markers. Join sleeve seams then side seams to top of garter stitch borders thus leaving small slits at side edges."
Again lay the sweater, now joined at the shoulders, out on a table and place the top of a sleeve (the cast off edge) next to the side of the sweater and center it at the shoulder. From the center of the shoulder, measure 6.25" down along the front and that's where to pin one top edge of the sleeve. Measure 6.25" down the back and pin the other top sleeve edge. Seam the sleeve to the sweater and do the same for the second sleeve.
Finally, sew the sleeve seam, sew the side seam. Leave the garter st border open at the bottom so that it forms a slit at the bottom of the sweater.