Double crochet (abbreviated dc) is a one of the basic crochet stitches.
At all crochet schemes double crochet symbol would appear as:
At the scheme below you can see a stitches of double crochet.
Double crochet instructions
Yarn over the hook and insert hook in the last stitch of the previous row under top two loops.
Catch the yarn.
Pull the yarn back through the loop. You should now see three loops of yarn on your hook.
Bring the yarn over the crochet hook from back to front and draw through the first two loops on the hook. You now have two loops on the hook.
Bring the yarn over the crochet hook from back to front and draw through both loops on the hook.
Repeat the process inserting hook in the following stitches of the previous row under top two loops.
Guide to Back Loop Double Crochet
Save this step by step tutorial as a reminder