Instructions of use, as found on the product package:

Moisten the stone with water. Using circular movements, grind both sides of the blade in the direction of the angle of the blade. A knife that is blunter than usual requires stronger handling. The mud emerging on the top of the stone helps the finishing process. Use plenty of water when sharpening harder and blunter blades.

Finally, grind the knife in straight strokes from both sides in a slightly steeper angle than when sharpening the blade (as if you are attempting to carve steel shavings). Remember to use the stone often, so that the blade does not become very blunt.