Beginner...need help with pattern

I am a beginner knitter (self taught) and just started to knit a pair of “easy arm-warmers”. They are a striped pattern (2 colors A/B) using stockinette stitch. I cast on 46 stitches and followed the directions for next 16 rows then it says;
"using yarn B, k1, s1 k1 psso, k to last 3 sts, k2tog, k1 (44sts). Work 9 rows without shaping. Work 10 rows in yarn A without shaping. Last 20 rows set stripe patt; 10 rows yarn B,10 rows yarn A."
I don’t understand the next direction…
Cont. working stripe patt throughout, at same time dec as set on next and foll 20th row (40 sts)**


These kinds of arm-warmers are a great project especially with the colder weather approaching.
The pattern wants you to continue the stripe pattern of 10 rows in each color. On the next row repeat the decrease at the beginning of the row (k1, s1, k1 psso) and also at the end of the row (k2tog, k1). Then on the 20th row again repeat the decreases.
That should bring your stitch count to 40sts.

That makes sense…thank you so much for your quick response!