Most crochet pieces will start with a length of chain stitches.
1 With the slipknot already on your hook, holding the hook horizontally in your dominant hand and gripping the slipknot with your yarn holding hand (if you are right handed this will be your left and if you are left handed this will be your right),
2 bring the yarn over the hook (yo) by passing your hook in front of your yarn, under and around it, rotate your hook towards you, draw the yarn through the loop on the hook.
To make a length of chain repeat from step 2. Try to keep your stitches neat and even for a professional finish.
See How to count your chain HERE
And How to make a Treble stitch HERE