Help understanding a Rowan pattern

I am knitting a sweater and working on the sleeves and the instructions are unfamiliar, please help:
Directions say: Dec 1 st at each end of the next 3 rows,
then on following 2 alt rows,
then on 3 following 4th rows,
then on 6 following alt rows.

Can someone please explain what rows to perform the decreases aside from the first 3 rows?
Thanks so much!

Welcome to KH!
These directions always seem complicated. It helps to write them out or write out row numbers and cross them off as you do them or use a row counter.
Including the first 3 rows, decrease on rows 1,2,3, then 5,7, then 11,15,19, and finally 21,23,25,27,29,31.