There are several probable causes to having cloudy water, and quite a few steps you can take to clean it. The utmost important thing to have when owning a fish tank [aside from the water, tank, and fish themselves] is a filtration system. You need a filter to clean the water, as well as to cause water flow. Standing water goes stagnant quickly, and soon becomes unlivable to the fish, additionally, water which flows becomes oxygenated. Fish draw oxygen out of the water with their gills in order to breathe, which is why an air bubbler is another important bit to owning and maintaining a tank, though not entirely necessary, but highly advisable. Another absolute must is tap water conditioner. It breaks down heavy metals and chlorine in the tap water, and makes it safe for your fish to live in. It is usually readily available at most if not all major pet stores, and I know for a fact you can buy it from your local Wal-Mart's pet section if they have one, being as this is where I got mine. An important part of setting up a fish tank is cycling it, which means you set up your aquarium beforehand, put in all the decorations and gravel and such, install the filter, fill it with water, add the conditioner, and let it run for anywhere between a day and a week or so. This is because when you first set up your tank and let it run, the nitrate levels spike and become toxic for fish. However, by the end of a week, the levels will have lowered, and the water will be safe. If you've done all this, and the water is still cloudy, it might just be the condition of the water in your area, so you could try using only bottled spring water in your tank. However, make sure it is bottled in a real spring, such as the Poland Springs brand, and not Dasani or Aquafina. I saw a special about water on Modern Marvels, and the Aquafina and Dasani brands of "spring water" actually come out of a tap. I do, however, only recommend this act as a last resort, as it's gonna tank a lot of bottles of water to fill the tank, depending on the size of it, and you'd have to keep buying new bottles every time the water level got low.
Additionally, if you're looking for advice about what are good breeds of fist for newbies, I've advice on that, too, however, that's a different question, and I won't go into detail about that here.