Each block has the degrees angle printed within the block. Place the guide on your sharpening stone face up so you can read the numbers then place your knife on top. That is the angle at which you will sharpen your knife. This is meant as a guide and isn't meant to be on the stone while sharpening.

Most Japanese knives come from the factory sharpened at 17 degrees. Most knives for the European/North-American market are sharpened at 19-29 degrees. Outdoors/camping knives can hold their edge longer when sharpened to 22.5 degrees.