You will need a double-sided (coarse and fine grit) synthetic sharpening stone. You will also need a honing steel, which is typically sold in the form of a lightly-grooved, magnetized iron rod. Both of these materials can be found at your local hardware store. Sharpening stones have two sides with different grits. The grit measures how rough the stone is, and thus how severely it sharpens. Higher numbers stand for finer grits meaning the lowest number is the roughest surface. This hand provides the control and keeps the edge down on the stone as you work.

Summary:
Gather the necessary materials. Hold the knife with the handle in your dominant hand so that your index finger is on the edge of the blade, almost where it meets the stone.