Pls h-e-l-p! Can't understand knit pattern

Hi!!!
I am new here and new to knitting! I can do a knit, purl (learned continental method) and love knitting! Crocheted 30+ years but love knitting!!

I bought yarn today and can’t understand this pattern. It says:

Row 1-14 garter stitch; knit every row. (so I gather this is just KNIT 14 rows right off the bat. Then…

Row 15: work 10 sts in purl, change to main color, work 20 sts st st. Change to cc work 5 st st. *repeat from * to * 5 times.

MY QUESTION: is the garter stitch just regular knitting???
and
How can I do st st just 20 sts??? I thought to get st st, you had to do ROWS of it…???

Oh I hope I’m making sense!!! Please please help!!! Thank you so much!!!

Row 15: work 10 sts in purl, change to main color, work 20 sts st st. Change to cc work 5 st st. *repeat from * to * 5 times.

Yes, 14 rows in garter st (knit every row).
On row 15, you’re setting up the patterns for some number of subsequent rows. You’re right that stockinette is a series of rows alternating knit one row, purl one row. So one way to do row 15 is purl 10sts, knit 20sts in main color, change to cc and knit 5sts and do the repeat. On the next row, the stockinette knit sts should be purled.

Here’s the exact goofy instructions…

With cc cast on 165 sts.
Rows 1-14 = garter stitch; knit every row.
Row 15 = with cc work 10 sts in purl, *change to mc work 20 st st. Change to cc work 5 st st. *repeat from * to * 5 times.

Row 16 = with cc work 10 sts in purl, * change to mc work 20 sts in purl. Change to cc work 5 sts in purl.* repeat from * to * 5 times.

Row 17-232 = repeat rows 15 and 16. (repeat row 15 for all odd numbered rows and repeat row 16 for all even numbered rows).*

Rows 233-246 = with cc work in garter stitch.

Sent from my iPad

Just ignore the st st instructions for row 15, and knit those sts. It may help you to understand that row 15 is the RS/right side, or the pattern side.
So purl 10 sts in cc, * knit 20 sts mc, k5 in cc, and repeat from * 5 times. For row 16 you’ll purll all the sts, changing the colors and that’s how you get stockinette when you knit row 15 and purl on row 16.