How do I use the Gathering Foot to gather fabric and attach it to a flat fabric at the same time?

Place the fabric to be gathered under the Gathering Foot right side up, then place the flat fabric into the slot from the left side opening with the right side down. Sew while keeping the two layers aligned, but do not hold them back as this would prevent them from feeding properly while stitching together. A longer stitch length and tighter tension will produce fuller gathers. (Page 15)