Dutch knitter here, I'll give a rough translation a try.
The petticoat consists of a waistband, hip part, and bottom part / skirt. Those are the 3 blocks in the diagram. All measurements given seem to be in centimetres for sizes S/M/L.
The diagram gives half of the total width of the pieces. So a hip piece for size S is 30 cm high, but 50x2 = 100 cm wide once you've knit it.
it doesn't give a yarn or gauge, just the measurements in cm. It tells you to find the right stitch amount for your yarn based on a gauge swatch.
Start with the hip piece: CO in red the amount of sts you need for the height of the hip piece (30/32/24 cm as per the diagram).
Then knit the hip piece in a wide rib stitch in red:
all needles in stockinette sts with red; needles 5 &6 in black are both knit to for a purl ridge. It's an 8 row repeat.
Continue until your hip piece is the desired width +4 cm when slightly stretched.
The skirt is knit in a zigzag pattern. The pattern repeat counts 12 sts, plus 2 sts for the edges.
CO in black, 12 times half the amount on ridges on the hip piece. For example, if you have 40 ridges, CO 12 x 20 = 240 sts.
In black: knit 2 rows, purl 1 row, knit 1 row.
Make the first zigzag in red:
- needle 1: *k1, yo, k4, k3tog, k4, yo, repeat from *
- needle 2: purl
Repeat these 2 rows a total of 6 times, then add a ridge in black:
knit 2 rows, purl 1 row, knit 1 row.
Make 3 zigzags or continue until the skirt portion has the desired length.
The waistband is knit in stockinette. Using black, pick up & knit from the hip piece the amount of sts you need for the correct waistband width (see diagram).
Knit stockinette for 3cm, knit 1 row on the wrong side (creating a purl bump ridge on the right side), then knit another 3 cm. Fold over & sew down, leaving a gap to insert the elastic.
Then sew the skirt & hip pieces together, and seam up the sides.
