Adult Surprise Jacket

Hi,
I'm new to the blog. My friend and I would like to make the BSJ for ourselves and could use some guidance from those who have done it. I saw the pictures and they're outstanding.
Thanks,
Pam

BSJ explanation

Ok, I feel myself stupid now. Don't understand: "At 5 ridges, increase 9 sts across end sections for fullness above cuff."
1. A ridge is a purl bumps? So 1 ridge means 2 rows in garter st?
2.Do I have to increase at the same time as before those ridges 2 sts at each end, making 2 diagonal lines? (probably yes)