Part of WoodenBoat’s Master Video Series, Louis Sauzedde (see WoodenBoat No. 239) gives a well-detailed and highly focused demonstration of how to sharpen a handsaw. Halsey Fulton of Fish Hawk Films shot the excellent close-up video of the action. (10 minutes)
If you want to learn more about saw sharpening, Keeping the Cutting Edge by Dynamite Payson is a great resource.