Here's how it works:

1. Firstly, make sure that you have the proper supplies. You will need a candle (beeswax is preferable), a feather, a wooden spoon and a paper bag.² Most Judaica stores carry "bedikat chametz kits," and sell them for under two dollars. Buying one certainly makes life easier. [The search is done by candle light, hence the candle. The feather allows you to sweep any chametz crumbs into the spoon, which is then poured into the paper bag].

2. Take ten pieces of bread, wrap them in paper so that no crumbs should escape, and disperse them around the house. It is advisable to write down where you placed the bread, because if you don't end up finding all ten pieces, you have to search again and again until you find every one...

3. After sunset light the candle, hold it together with the feather and paper bag, and recite the following blessing: Baruch atta Ado-noy Elo-hai-nu Melech ha'olam asher kid-sha-nu b'mitz-vo-sav v'tzi-vanu al bee-ur chametz. [Blessed are you, Lord our G-d, King of the universe, who has sanctified us with His commandments, and commanded us to remove the chametz.]

4. Proceed to search for chametz in all the rooms of your house. Any chametz which is found, and the ten pieces which you spread around, should be placed in the paper bag.

5. Don't speak after reciting the blessing before starting the search, as this would constitute an interruption. Also for this reason you should commence your search in the same room where the blessing was said. It is actually preferable to avoid speaking throughout the search, this way you won't be distracted from performing a proper search -- however, you may speak if necessary as long as you already started the search.

6. When you finish the search, place the extinguished candle and feather and the wooden spoon together with the chametz in the bag. Close the bag securely and put it in a safe place until it will be burnt tomorrow morning.

7. Immediately after the search say the following: All leaven and anything leavened that is in my possession, which I have neither seen nor removed, and about which I am unaware, shall be considered nullified and ownerless as the dust of the earth.

See also Exactly which locations must be included in the ceremonial search for chametz?