I'm going to respectfully disagree with Ben here; in general white smoke is indicative of coolant being turned into steam inside the engine, which is usually caused by a blown head gasket. Other causes are possible, but that's the most common. Burning oil as a result of failed piston rings is normally black rather than white.
This can be caused by a number of factors, but a common one is overheating the engine causing the cylinder head to warp. This isn't a situation where any kind of service can fix the problem; it would require removing the cylinder head, possibly reconditioning it and replacing the head gasket. These are major repairs that require a significant amount of automotive repair skill to do properly.
Has anything happened to the engine recently such as it overheating or being run low on oil? Has it been using oil or running out of antifreeze? Odd noises or loss of power? How many miles does the engine have on it?
Give us a little more information and we'll see if we can help you figure out what to do.