Foundation crochet stitches are an invaluable skill to learn in crochet. They are simple to learn and offer the benefit of creating you starting stitches all at once without having to make all of your chains first. Foundation stitches are wonderful for when you are not sure exactly how long to make your starting round or row, or are wanting perfectly even tension and stretch between the top and bottom of the stitches (starting with chains will result in the bottom of each stitch being much tighter than the top of the stitch).
STEP 1 (the first fdc):
Chain 2, yarn over and insert your hook into the second chain from the hook and pull up a loop, yarn over and pull through 1 loop only (you have just made a chain), yarn over and pull through 2 loops, yarn over and pull through the the remaining 2 loops on your hook. You have just completed your first foundation double crochet stitch.
STEP 2 (subsequent fdc): Yarn over and insert your hook into the bottom 2 loops of the previous stitch (the chain), yarn over and pull through 1 loop (you have just made a chain), yarn over and pull through 2 loops, yarn over and pull through the remaining 2 loops on your hook. Your second foundation double crochet stitch is now complete! Continue to repeat STEP 2 until your foundation row reaches your desired length.