A plasma cutter works by super-heating gas until it becomes plasma, in which the atoms are ionized. An electric charge passing through the gas to the metal to be cut forms an arc of energy that is so hot it melts the metal. Since the arc is tightly focused by a thin-tipped nozzle, the plasma cuts through the metal. In most plasma cutters, there is a baffle, which regulates the flow of the plasma and causes it to swirl. This allows the cut to have a smaller kerf, or angle. In addition, the part of the gas that is not ionized pushes the molten metal out of the way so that the cut is cleaner.
Different models of plasma cutters are designed to use a variety of electric sources; you'll need to check whether you have the appropriate voltage for the cutter you're using. Some types can be adjusted for use with the varying voltage in different countries or from different generators. The current on the machine is adjustable, so you can choose the power level you need.
The power of your plasma cutter can be determined by multiplying the voltage by the amperage. For instance, when you use a 12-amp cutter with a 110-volt power source, you will have up to 1,320 watts of cutting power, which can cut through quarter-inch steel [source: Miller].
Generally, when you begin a cut, you should start with the amperage or current set at the maximum, then adjust downward to the appropriate level for what you are cutting. You will need to use a greater current on thicker or harder metals, and also when you want a small kerf or very precise cutting. You can use less power and a slower cutting speed when precision or neatness is less important.