A ywfd is the same as a YO in this case. So you knit into the stitch but don't slip it off the left hand needle, and then bring the yarn to the front of the right hand needle between the needle tips and over the right hand needle to the back again. From there knit the stitch again. Now let the stitch off the left hand needle. This made 3 stitch loops where you had one, the middle one being the yarn over.