A spoke-wrench, in the wrong hands, is easily the most expensive little tool anyone can own. Read up thoroughly on the subject before use. It's not rocket-science, but it does require dedication and an understanding on what, why, and how you're about to true a wheel. If you tighten one spoke on one side of the rim - loosen the other spoke opposite an equal amount. Generally 1/8th to 1/4 of a turn.

Good luck! It's is a lot of fun once you get the technique down.