The walking foot is often described as a sewing machine foot that evenly feeds layers of fabric and batting through the machine while quilting.
The foot grips onto the top layer of fabric and helps move it under the needle at the same pace that the machine's feed dogs are moving the bottom layer of fabric Every walking foot has a fork or extension or bar that rides on the needle clamp screw. As the needle bar moves up, the walking foot moves and feed dogs engage. A walking foot has its own feed dogs on the bottom. These work together with the sewing machine's feed dogs and help to pull the quilt sandwich layers evenly through the machine. Walking Feet are not for use in reverse or side to side sewing as well as some built in stitches that include other than forward movement of the feed dogs. This is a mechanical foot.
It wears out with use.
I know because I've replaced a foot due to oodles and oodles of ditch and straight line quilting.
How to tell?
If the foot and it's feed dogs don't move as the needle clamp screw goes up and down, it is broken.
The arm (sometimes it is more like a fork) is the weakest part, so do take care where you store it to extend its useful life.