FDC – Foundation Row Double Crochet: Ch3, yo and insert hook into third chain from hook, pull up a loop (3 loops on hook). *Yo and pull through 1 loop (this creates the base stitch (chain) for the next fdc), you should still have 3 loops on your hook. Now complete a dc stitch (yo and pull through 2 loops, yo and pull through 2 loops again to complete the dc stitch). To start the next stitch, yo and insert hook into the ‘v’ of the base stitch, yo and pull up a loop (3 loops on hook), yo and pull through 1 loop on hook (chain created), now complete a dc stitch as before. Continue this sequence for the number of stitches in your desired width.
The ch3 at the beginning of your Foundation Row counts like this: 1 chain is the chain stitch and the other two chains are your first DC of Row 1.
Below is a quick video tutorial of how to do a Foundation Double Crochet (FDC) which I recommend in all my patterns instead of a chain start method.