The piping foot is sometimes also called a cording foot. This sewing machine foot is used to attach piping to fabric. When you look at the foot, you see a small hole in the top of the foot, where the needle passes through. On the bottom of the foot is a groove. The foot comes in two sizes, 1/8 inch and 1/4 inch. The groove in the bottom of the foot corresponds with the the diameter of piping.
The needle hole falls right at the edge of the groove, so as you sew the fabric around the piping, the stitches are placed right along the edge of the piping.
The following link is to a video I created demonstrating the piping foot being used to make piping. The process is very simple. I cut 1 1/2 inch strips of fabric that I want to use to cover the piping. The fabric strip is then wrapped around the piping. The fabric wrapped piping slides into the groove of the foot and then you sew.
When you start attaching the piping you should leave the first couple of inches free, start stitching in several inches from the end of the piping.
As you reach the end of your project, again stop stitching leaving several inches of the piping loose.
Allow the two ends to overlap. Trim one side of the overlapped piping about an inch into the overlap.
Trim the other side even with the fabric covering.
Next, open up the seam you sewed to make the piping to expose the inner piping cord. Line both ends of the piping cord up once again and trim the piping to be the exact length required, both ends should end touching each other.
Now bring the fabric back over the piping, folding under the raw edge to create a finished edge. The fabric will overlap slightly. Once you have the piping realigned, line the piping up in the groove under the foot and finish stitching the piping in place.
With a little practice, you will become an expert at using the piping foot. Making your own piping will allow you to add sorts of interesting detail and contrast to your projects. Go ahead and give it a try!