What kind of cloudy? Is it milky white, or does it have a green tint to it? How long has the tank been setup? Is it cycled? What kind of fish do you have?
Answers to these questions will help give you a more definite answer, but most likely it is just a bacteria bloom. It happens with newly established tanks. It looks unsightly, but it will not hurt the fish. There is no way to get rid of it quickly. You just need to let it run it's course. It may last a few days or a week. Resist the urge to buy any water clear type chemicals. They would help very little, can be detrimental to your system, and would just be a waste of money.
Remember that Almost nothing good happens FAST in an aquarium.