Tippit,
Thanks. The flatter is used to flatten an area of the blade called the Ricasso. You just hold it on the area to be flattened and hit it with the hammer. Of course, the anvil needs to be flat as well.
Nearly all hammers have a curved face and although you can do a pretty good job of flattening just with a hammer, the flatter does a little better. Flattening the Ricasso provides a baseline to reference the whole blade's straightness. It also keeps you from having to grind away too much material in an attempt to grind the blade straight.
In the sunshine, the blade dont look very hot, but it was hot enough to move a little. I like to reduce forging heat in the straightening phase of forging a blade. This refines the grain structure, which is good for the blade.
Incidentally, the flatter in the picture belongs to Big John Fitch MS. He came up with an ingenius idea of having the flatter head fitting very loosely on the handle, with a keeper pin out in front of the head. This allowed the head to truely flatten the work piece and not be influenced by the handle being held, perhaps, at a bad angle. Reduced handle shock too.
Lin