Looks like an axe stone. Can't recommend a good tutorial other than a scout who knows. But you might find some. The key is a grip that keeps all your fingers on the rim and away from the side you're using.
Definitely an axe stone, I have one like it for keeping my American woods axe keen for limb lopping and light felling.
You could use it to sharpen a pocket knife, but they are usually too rough to get a fine edge. Fine for a knife that does rough work like a woods knife, but a pocket knife should be sharper than the stone can do.