Used to pull dents out of metal panels when you can't push it out from the back side.
To use load stud in gun. Press against bare metal and it automatically turns on to weld the studs on. Then pull the dent out with the included slide hammer. After pulling the dent cut off the studs & sand it smooth before repainting.
It actually worked really good, better than I expected.
The last two pictures are from the manufacturers website, so you can see how it works.
It includes a bunch of studs in a zip lock bag.