The treble crochet is a very tall stitch [single crochet beeing the smallest one].
From the chain, wrapping the yarn twice around your hook, skip the first four chains and insert the hook into the fifth chain from the hook.
Bring the yarn over the crochet hook and draw it through the first two loops on the hook to get three loops on your hook. Repeat the process to keep two loops on the hook and finalize the stitch.
For more detailed explanations, clear illustrations and a video, go to Annie’s Craft Store. She has a wonderful stitch guide!