Can someone please help me understand?

#1

I January (!) I started knitting a dress for my niece. This is my first time knitting by american instructions (I am Norwegian), and I am really struggeling.
This is the pattern, and I am knitting size d.
https://www.lovecrafts.com/en-us/p/flore-dress-in-phildar-phil-coton-3-122-downloadable-pdf

I am working on the frill in front of the dress now, but I don’t understand how the instructions can lead to the wave effect… Can anyone please help me?
I have completed the 6 rows, but what to do next?

FRILL
Using 3 mm needles and POUSSIN, cast on a) 156 - b) 176 - c) 198 - d)
216 - e) 256 sts and work 6 rows in st st; then on foll alt rows, leave sts on
a holder as follows: a) 26 sts 5 times - b) 29 sts 4 times and 30 sts once - c)
33 sts 5 times - d) 36 sts 5 times - e) 42 sts twice and 43 sts 3 times
Knit 1 row on all sts, then cast off sts in pairs.

#2

The idea is a bit like binding off sts for the shoulders of the back on a sweater. Instead of binding off the sts, the sts are placed on holders.

After you work the 6 stockinette rows on 216sts, knit across 36sts, place them on hold, finish the row and turn. Purl 36sts, place them on a holder and work to the end of row. Repeat these steps until you have 5sets of 36sts on holders and 36sts on the needles. Then knit one row across all the sts and cast off.
This should give you a “hills and valleys” ripple effect for the ruffle.

You’ve done very well with this so far. I’m not surprised that this part is difficult to understand. It’s not so clear in English.