This presser foot is used for holding a button in place and attaching it using the zigzag stitch.
Be sure to first lower the feed dog so the fabric is not fed and adjust the zigzag width so the needle enters the holes in the button.
To create a shank for the button, insert an awl or another similar object into the groove in the presser foot before sewing on the button so that the stitching will create a loop suitable for the thickness of the fabric.