To make the double crochet stitch, wrap the yarn around your hook.  Skip the first 3 chains, remembering that the loop ON the hook does not count as a stitch.  Insert the hook in the center of the 4th chain stitch.  Wrap the yarn and pull it back through the chain stitch.  You now have 3 loops on your hook.

Wrap the yarn around the hook and pull it through the first 2 loops.  Then wrap the yarn once more and pull it through the remaining 2 loops.  Continue working down the chain, working every chain stitch.

When you reach the end, chain 3 and turn your work.  Wrap the yarn around your hook, insert your hook in the next stitch under both of the top loops.   Wrap the yarn around the hook again, pull through the stitch.  You now have 3 loops on the hook.  Wrap the yarn around the hook and pull it through the first 2 loops.  Then wrap the yarn once more and pull it through the remaining 2 loops.  Continue working the pattern until your piece is the desired length.