According to USA Today, a taser emits 50,000 volts. The voltage impairs the muscles and renders a person immobile. Taser guns can be fired from a distance of 35 feet.
USA Today further adds that taser guns have wires with small barbs attached to the end to penetrate the skin. HowStuffWorks notes that the barbs contain electrodes that go into effect when touching the skin. Electric currents travel through the wires and electrodes, incapacitating an individual. Distance is an advantage with taser guns, but shooters only get a single shot.
Tasers are classified as nonlethal, but many have died as a result of being shocked, according to USA Today. Wikipedia notes that tasers can lead to cardiac arrhythmia in people who have heart problems, which can lead to sudden death.