This is the second video (again for beginners) to show how to cut an edge of a piece with a hand saw effectively. (Sorry it’s still in Japanese.)
In the first half, one edge is cut off. In the second half (from around 4:18 onwards), a few more edges are also cut to form a mountain-like shape (though I didn’t realize such an intention of my father until the shape became obvious!).
“Part 3” is a demonstration using a vise (vice) and saws!