Submerge The Whetstone
You need to submerge the whetstone for five to ten minutes and when the air bubbles stop coming the stone has absorbed the optimal amount of water. Continue to apply water while sharpening as it combines with small particles in the whetstone to form an abrasive substance which causes the sharpening to take place.
Place the stone on an anti slip base and start by using the coarse grit of the stone. Move the blade back and forth at an angle of about 10 to 15 degrees across the entire stone. Make sure to use light pressure and start at the tip of the blade and work it down towards the base of the blade. After a short while a fine edge will be developed. Now turn the knife around and work on the other edge of the blade. Repeat the same process several times as necessary and it is very important to always maintain the same angle. To finish pull the blade twice at an angle to the cutting edge to remove the last burrs and it should then be really sharp.
Rinse off the whetstone to remove the grinding residue and rinse the knifes carefully in hot water.
There are fixed standards for grit sizes that apply in different parts of the world and it is not something you really need to worry on.