Clouds of white smoke can indicate one of two things:
1. Coolant leak from head gasket into a cylinder; or
2. a new pope has been elected.
Guessing 1, above, I recommend towing the car to someone qualified to do a leak-down test on the cooling system. That should give the answer.
If you have led a good, clean life the problem should not be too expensive to resolve, guessing about $500 for replacement of head gasket. If you haven't, you may have a warped head, scored cylinders or worse.
One other indicator might be the presence of a milky white substance in the oil. Check your dipstick. Absence of same is not conclusive.