Chametz is a term for any food that is not kosher for Passover. The rules for observing Passover are very strict regarding not having any Chametz, even tiny crumbs, in your home during the holiday, and so there is a lot of significant house cleaning that goes on prior to the holiday. I like to joke that the Jewish people were the ones who invented spring cleaning.
So, we thoroughly clean the house, and remove all the Chametz. Modern Jewish law allows for the “selling” of Chametz. This practice consists of a family storing supplies of Chametz and dishes, pots, pans, etc, somewhere that will not be accessed during the holiday, and then with the help of a Rabbi, drawing up a contract that sells this storage location to a non-Jew, who will hold onto it for the length of the holiday, and then return it after Passover is over. It is a legal loophole so that preparing for Passover does not become an undue financial burden on a family.
After we believe we have rid the home of all the Chametz, on the night before the first Seder, we perform a ritual search, called Bedikat Chametz, to ensure we’ve gotten every last crumb. To make sure we are not saying a blessing in vain, we hide ten pieces of Chametz around the house, to make sure we have some Chametz to find during the search. We then say the appropriate blessing (see link below), and perform a search around the darkened house using a candle for light, and a spoon and feather to sweep up the discovered Chametz. We put the found pieces of Chametz in a paper bag, so that it is ready to be burned along with any leftover Chametz from breakfast the next morning.
The following link is to a Rabbinical Assembly handout with instructions and the blessings used for Bedikat Chametz: http://www.rabbinicalassembly.org/sites/default/files/public/jewish-law/holidays/pesah/b-dikat-hameitz.pdf