A fringe foot (also known as a looper foot or tailor tack foot) is a great addition to your sewing toolbox. With just a zigzag stitch, you can incorporate a lot of decorative, textured looks to your projects.

The most important feature is that raised central bar. When you sew using a zigzag or similar stitch , that bar allows more thread to go in each stitch. Thus creating loops, which can be manipulated to create fringe.
The extra thread creates wider loops of thread. Because of all this extra thread, the foot is open in the center-bottom portion to avoid the thread getting caught.
In the front of the fringe foot, you see a pronounced V shape. Use the tip of the V to guide the fabric so the loops are perfectly positioned.

It also works well for appliqué, embroidery and other decorative stitches.