Can I Please have some confirmation of the correct understand of knitting pattern?

I am making my first jumper. All I need is some clarification from an experienced knitter.

The section of pattern in question is this:

Using 4.00mm needles and CC, cast on 40 (42-44-46) sts.
Working in garter st (1st row is wrong side), inc one st at each end of 21st and foll 6th (6th-4th–4th) rows until there are 50 (60-52-72) sts, Sizes S and L Only - then in foll 8th (6th) rows until there are 56 (64) sts.

If anymore information is needed, here is the link to my pattern:
https://www.spotlightstores.com/projects/knitting-crochet-projects/marvel-soft-garter-stitch-jumper-project

I am making the small size.

After I cast on, will I simply knit in garter stitch for the whole thing and increase on both ends of the 21st, 27th, 33rd, 39th, 45th, 53rd, 61st and 69th rows?

Your help would be greatly appreciated.

Thanks
Sarah

Welcome to KH!
Thanks so much for the link and the size information, a big help. Yes, all garter stitch and yes, you have the correct rows for the increases. Congrats on your first sweater.

Thank you!!!