From the pattern:

This pattern includes sizes S (43 - 48 cm), M (48 - 53 cm) and L (53 - 58 cm) - sizing is achieved by using different yarn weights..

Gauge for S: 24 sts / 10 cm
Gauge for M: 22 sts / 10 cm
Gauge for L: 20 sts / 10 cm

Sample is knit from 6ply sock yarn on needle size 3.5 mm

Choose yarn and needle so you get the correct gauge.

Pattern includes a picture tutorial for the crochet flowers.