The free-motion quilting foot, sometimes called a darning foot or hopping foot, is designed so that the sewing machine needle passes through a small ring on the foot.
If you want to do free-motion quilting, your regular presser foot won’t get the job done because it puts the machine in control.
A regular sewing machine foot provides downward pressure on the fabric, holding it against the feed dogs as you sew. As a result, the feed dogs pull the fabric along with each stitch. That means that the machine has complete control over how the fabric moves.
When free-motion quilting, you want to be in control. By using a free-motion quilting foot and disengaging the feed dogs, your quilting will be completely self-guided.
A free-motion quilting foot also provides plenty of visibility. It’s important that you can see the quilting design right around the needle so that you can shape your stitches well. Most presser feet are bulky, but a free motion quilting foot covers hardly any of the quilt.