If you are experiencing a wobble on a bicycle wheel, it has likely gone "out of true." True refers to the alignment of the bicycle wheel, usually maintained by even tension on the rim by the spokes. When spokes loosen or when the rim takes a hard hit, the wheel can wobble if the rim deforms to reflect uneven tension from the spokes. Bring the wheel back to true to correct the wobble.
Remove the offending bicycle wheel from the bicycle. Most wheels use a quick release levers. Pull down on the lever and turn counter-clockwise to loosen and then remove the wheel from the forks.
Mount the wheel into the truing stand. Be sure the stand is on a flat work surface. The truing stand has a set of calipers. Place the wheel between the calipers and push the wheel hub into the hub cradle to secure it to the stand. Bring the calipers to within 1/4 inch of the wheel.
Stand behind the wheel and turn it. Watch the gaps between the sides of the rim and the calipers. When the wheel moves laterally, changing the gaps at the calipers, stop the wheel and use your finger as a placeholder for the location of this wobble.
Place the spoke wrench over the nipple of the spoke nearest the wobble and on the side of the wheel on which the caliper gap became wider. Turn the wrench 1/4 turn clockwise and remove. Spin the wheel again and watch as the rim moves past the calipers. You may need to make additional 1/4-turn adjustments to the same spoke and to the adjacent spokes on the same side of the wheel until there is no lateral movement and the wheel is back in true.
Remove the wheel from the truing stand put it back on the bicycle. Take a test ride to confirm that the wobble is gone.