This is a brilliant stitch for outlining things. I use it to give my realistic animal ears a nice raised edge that I can sew into and make it seem to pop slightly from the fabric. You need two threads, a thicker one for the base (this is your foundation thread or 'laid' thread) and in the diagram above it is the light pink line. You will need a thinner strand of thread (maybe two strands of embroidery floss) and this is the 'couching' thread, the dark pink line in the image. In the instructions I will refer to them as 'foundation' and 'couching'
Cut a length of foundation thread, the length of your outline plus enough on either end to secure it to the fabric. Use a needle to bring your foundation thread up through the fabric where you want to start your outline and lay this in the general direction of your outline. You can remove the needle for now.
With your needle threaded with the couching thread, bring it up through the fabric and make a small stitch over your foundation thread as close as possible to the entry hole of the foundation thread. Now, continue to make evenly spaced couching stitches along the length of your foundation thread.
Don't forget to keep an eye on the foundation thread and make sure it's following the line of the outline that you want. When you are nearly finished with your couching, thread your foundation thread and go into the fabric at the end of your outline.
Do your last stitch as close to the end of your foundation stitch as possible and then secure your last couching stitch on the back of the fabric.
You can space the couching stitches as far apart or as close together as you want.