I need help understanding a knitting pattern please

I have been knitting a jumper but have come to a section of the knitting pattern that I am struggling to understand. The pattern says:
SHAPE NECK
1st row - (RS) K2, sl 1, K1, psso, K12 (17-21-24) turn.
Cont on these 15 (20-24-27) sts, for left side of neck shaping.
Dec one st at armhole edge (as before) in foll alt rows 1 (7-13-16) times, Sizes S and
M Only - then in foll 4th rows 4 (2) times,
All Sizes - AT SAME TIME dec one st at neck edge in foll alt rows 7 (7-5-2) times, then in foll 4th rows 1 (2-4-7) times … 2 sts.

I do not understand where it says turn, cont, foll 4th rows or foll alt rows.

Here is the link to the pattern:
Https://www.spotlightstores.com/projects/knitting-crochet-projects/marvel-soft-garter-stitch-jumper-project

Some help from an experienced knitter would greatly be appreciated.

Thanks

Welcome!
Which size are you making?

I wasn’t expecting such a quick reply, thank you!

I am making the small

The first decrease row is given to you. Then dec at the armhole edge on rows 3,7,11,15 and 19. On the neck edge dec on rows 3, 5,7,9,11,13,15,and 19.

Thank you salmonmac!

Now I can get back to my knitting!