The double crochet (dc) is a great stitch to quickly add height to a row. One dc row usually equals two single crochet rows.
How to make a dc stitch:
1. Yarn over hook (yoh). Always wrap away from you, up, then toward you. Some say, back-to-front.
2. Insert hook into next stitch. Unless directed otherwise, always insert under both loops of the stitch. Yoh and pull the yarn you just wrapped around the hook through the stitch. Three loops on hook.
3. Yoh and draw the yarn you just wrapped around the hook through two loops. Two loops remain on hook.
4. Yoh and draw the yarn you just wrapped around the hook through two loops. One loop remains on hook. One double crochet made.
To make another double crochet, repeat 1-4.