As others have said, it is a much larger pressure foot that moves with each revolution of your machine to duplicate the bottom feed dog action on the top of your fabric. It works well to help move all three layers of your quilt sandwich together to prevent one layer from slipping or dragging which will eventually cause distortions or puckers in your quilt stitching. I recommend you buy a good one, preferably the same name brand as your machine. A good one will cost $40-50. There have been lots of past discussions here about cheap generic walking feet that break easily which will just waste your money. It is very important to install it correctly on your machine, it should come with instructions, but there is an 'arm' on the walking foot with a prong on the end and you have to attach it so that prong slides on your needle bar of your machine such that the arm will move up and down with your machine action. Otherwise it fits like any other pressure foot. I think a walking foot is as necessary for quilting as a needle and thread--could not do without it!!