A steek is a reinforced area of tubular knitting, which is cut to insert a sleeve, front bands, or neckline facing. In this case, I'm inserting a sleeve. This sweater is knit from fingering weight yarn. The sleeve has 1/2" of reverse stockinette stitch at the top. You may be able to see it in the photo below. There also is an extra row of main color after the last pattern, which will serve as seam allowance.
The body is a tube. To figure armhole placement, divide the total number of stitches by 4. This sweater will be a cardigan, so the center front is an obvious steek area of 6 stitches, making determination of the center front easy. Count off 1/4 of the total stitches on either side of the center front, and mark at the top. Lay the sleeve on the body to mark the depth of the armhole. Both points are marked with pink embroidery floss. In this case, the pattern can be used to guide placement and ensure that
both sides are the same.
I am using only 2 stitches for the armhole. This means that a very narrow area of one whole stitch will be machine sewn. Both inside and outside are shown.
After sewing both sides of the center, cut between the lines of stitching.
Place the sleeve into the opening, pinning to prevent movement. You see the facing beyond the cut edge.
I chose to sew this one with an outline stitch, which has some stretch. The needle goes through the sweater one stitch from the cut edge. It goes through the sleeve where the stockinette and reverse stockinette meet. I do a 3/8" long stitch on the body side, and back up 1/8" to stitch the sleeve side. Continue around the sleeve.
Before stitching down the facing, the shoulder seam must be closed. Mark where the neck opening will start and the shoulder seam will end. I am using a crochet version of the 3 needle bind off. I put a crochet hook through the first stitch on the front and the back. Pull a loop through both stitches. Repeat and pull the loop through all three loops on the crochet hook.
Note that the yarn is wrapped clockwise when crocheting. At some point, you will need to transfer front or back stitches to another needle. The body circular will be too long. Continue working stitches from the front, back and hook until you reach the neckline marker.
When the shoulder is sewn, you can sew down the sleeve facing and cover the raw edges. Make sure that these stitches do not show on the right side.
Admire your beautiful sleeve.