While not required, creating a slurry on the stone before you begin helps polish the edge of the knife or tool.  In addition, this process slightly flattens the stone and prepares it for the final step in the sharpening process.

To create the slurry, wet both the slurry stone and the stone you’ll use for sharpening. Rub the slurry stone in a circular motion over the stone until the slurry is created.