How to make a foundation double crochet stitch (fdc) or if you're using US terminology, foundation single crochet (fsc) ::
I love using this stitch and it's counterparts (fhtr and ftr) because it creates a much more flexible foundation row for your crochet stitches than the traditional row of chains, it's also a really good way of starting a project if you want to turn and work into the underside of the stitches as it creates really clear loops in which to work into on the underneath. It's also really easy and in my opinion much quicker than the chaining option.
I've put together a little video showing you how to construct the the stitch ::
Patterns of mine that use this stitch can be seen below (click on the picture to be taken to the pattern details) ::