Aquarists add wood to their aquariums for many reasons. Some seek to emulate the natural environment of the fish they keep, some want to help buffer their water in a natural way, and others use wood as natural shelter for their fish. Whatever the reason, there are many benefits to adding wood decor to your tank.
I have seen many questions by novice aquarists about what wood to use, when to use it, and how to prepare it for the tank. The latest issue of the Tropical Fish Hobbyist contains a great article about driftwood where many of these questions are answered.