You need to know basic knowledge in crocheting:

magic ring
stitch
slip stitch
chain
single crochet
half double crochet
double crochet
increase
decrease
back/front loop only
row
round

Dimensions:

The landdragon will be around 19 cm lang, 7 cm wide and 3 high.

The waterdragon will be around 10 cm long, 7 cm wide and 3 high.

If you crochet with a different needle hook than 2.5 or different yarn your dragons will be bigger or smaller.

Materials:

Yarn: Use the colors and size you prefer and the matching crochet hook.
I’ve used crochet hook in 2.5 and three different cotton yarn by hobbii cotton friends 8/4:

Soft stuffing
A pair of 6 mm safety eyes (if you choose another yarn, you will perhaps need different eyes)
A needle and some black and white yarn for embroidering, sewing pins, scissors, stitch marker
(optional)