Slipknot

To make a slipknot: 

a) Wrap the yarn around your finger twice

b) Pull the back loop (1) over the first one (2)

c) Take (2) and pull it over (1)

d) Slide it off your finger, making a noose for your crochet hook

e) Insert the crochet hook through it

f) Tighten it by pulling the yarn threads (not too tightly so you can make the first stitch).