Sew shoulder seams. Place markers 4 (4, 4½, 5) in. [10 (10, 11.5, 12.5) cm down from shoulder on Front and Back. From RS, pick up and k 26 (26, 30, 32) sts between markers. Work in garter st (k every row) for 2 in. [5 cm].
Those are your directions.
So sew the shoulder seams together and then measure 4 inches down from the shoulder seam on the front pieces (on each side and place some sort of markers there). Then measure 4 inches down from the shoulder seam in the back on each side and place markers there. So now you will have 2 markers on the left side with 8 inches between them, and ditto on the right side.
Now you pick up 26 stitches for the left sleeve between the 2 markers on the left (as it will be when worn), so it is saying only 26stitches over the whole 8" width of the sleeve. Knit the sleeve by the directions given. Then do the same on the right side. Then sew the side and underarm seams.