another way of writing that would be:
row 1 - k all st
row 2- k4, p to last 4 st, k4
Repeat these 2 rows 19 more times.
this would give you 40 rows of stockingette stitch with a border of garter at either end. Garter stitch is created by knitting every row, and stockinette is created byt he alternating rows of knits and purls.