A knife is an effective cutting tool only if it's sharp. The edge of a knife dulls with use and must be sharpened. A knife sharpener straightens out the edge of the blade and shaves away a small amount of metal to cut a new edge. There are many types of knife sharpeners, but a ceramic-rod knife sharpener is one of the easiest to use. Rods are installed in a wooden base and are angled to put the correct angle on the blade.
Place the base on a solid surface, such as a table, and insert the ceramic rods in the predrilled holes in the base. The rods will form a "V" shape. Some bases have multiple holes drilled at multiple angles; choose the one that has the angle you want for your blade.
Hold the knife as vertically as possible, and make a slicing motion down one of the rods. Go from the top of the rod to the bottom, and from the heel of the blade (nearest your hand) to the tip.
Make multiple passes, then carefully test the edge by dragging your thumb across the flat of the blade toward the edge. The sharpening action should have raised a rolled edge, call a burr. If it hasn't, repeat sharpening one side until you raise a burr.
Move the blade to the other ceramic rod (the other side of the "V") and repeat the sharpening process until you raise a burr again, this time on the opposite side.
Continue sharpening side to side until you've achieved the desired angle.
Stretch out the leather strop (a belt also works) and drag the edge of the blade backward (not in a cutting motion) across the leather. Repeat on both sides until the burr is polished away by the leather.
Knife-edge angles are different depending on the application. For example, a fillet knife requires a shallow edge of 15 or 20 degrees per side. A utility or hunting knife may require 30 or 35 degrees per side.