i just wondering what wrong with my car with white smoke out of the muffler?? is there something wrong with my Radatior or water pump or need new oxygen sensor?

There might not be anything wrong with it if you're not losing coolant. Water is one of the byproducts of combustion, so it's not uncommon for it to collect in the exhaust, where it turns to steam because of the heat. It takes a finite time for this to take place, however, so repeated short runs at low speeds will often allow it to accumulate and produce excessive amounts. Condensation due to the difference between the exhaust and ambient temperature is another source. So is using cheap gas, which makes the pollution controls have to work harder.

If you are losing coolant, however, (check both the radiator as well as the overflow tank) suspect a cracked head or a leaky head gasket.

Does it occur only when starting up? Or is it continuous?

If it happens when you start up the car, and then stops smoking after you've driven the car for at least 1-2 hours, then that is an indication of condensation. you shouldn't get worried about this.

If the smoke occurs continuously then you have oil leaking into your cylinders. Change your gaskets.

does the smoke linger (oil) or dissapate quickly (water).