The Torah tells us:
Eat matzahs for seven days. By the first day, you must have your homes cleared of all leaven. Whoever eats leaven from the first day until the seventh day will have his soul cut off from Israel. The first day shall be a sacred holiday, and the seventh day shall [also] be a sacred holiday. No work may be done on these [days].
The only [work] that you may do is that which is needed so that everyone will be able to eat. Be careful regarding the matzahs, for on this very day I will have brought your masses out of Egypt. You must carefully keep this day for all generations; it is a law for all times. From the 14th day of the first month in the evening, until the night of the 21st day of the month, you must eat [only] matzahs.
During [these] seven days, no leaven may be found in your homes. If someone eats anything leavened his soul shall be cut off from the community of Israel. [This is true] whether he is a proselyte or a person born into the nation. You must not eat anything leavened. In all the areas where you live, eat matzahs.
— Exodus 12:15-20
The Torah commands us (i.e., Jews — this does not apply to Gentiles) not to eat any chometz or chometz derivatives from the day before Passover until Passover ends. Not only may we not eat it, but we may not derive any benefit from it during Passover. This applies even to items like soap and deodorants and other things.
The Torah further commands us not to even have in our possession such items, and if we have them on our property, they may not belong to us, and they must be put away.
It is also forbidden to use utensils (such as pots, pans, dishes, cutlery, silverware, flatware, etc.) that have been used with chometz. Some things can be made kosher for Passover, and we shall, Hashem willing, learn about that.
Therefore, we are required to remove all chometz from any and all property, including one’s home, office, car, locker, storage units, pockets in clothing, and so forth. This includes mixtures that may contain even an infinitesimally small amount of chometz within them.
If you own any chometz during Passover, it becomes forever forbidden to use, even to sell afterwards to a Gentile. Even after Passover has ended, you may never use this chometz for anything at all, forever. You must destroy it.
However, before Passover starts, your chometz may be sold to a Gentile according to special arrangements done by local Rabbis. The chometz must then be put away in a place you will not use or access during Passover at all, but in a place where the Gentile may come and take them if he wants to. (It may be in your home or storage place, however, locked away safely.)
This must be an actual sale, not, as many people mistakenly think, a “symbolic” sale, whatever that means. The chometz must actually belong to the Gentile, and if he or she comes to take it, you must show him or her where it is and allow him to take it by himself or herself. You may not touch it or pick it (or ANY chometz) up during Passover, but the Gentile must be allowed to access and take it if he or she requests it.
The sale is created, however, to be temporary. After Passover, the Rabbi must buy back the chometz from the Gentile, and then we may use it again.
Do not attempt to make this sale yourself. The means by which the sale must be done and many other details are quite complicated.
Note that we do not sell dishes, pots, pans, etc., that were used for chometz. What we sell is any chometz that we have not been able to eradicate, that might be in those utensils. (If you sell any actual utensils used for food, when you get them back you will have to immerse them in a mikvah.)
Chometz must be removed entirely from one’s home, as best one can. We clean our entire homes, and then we must search for any chometz that we might have missed.
Anything that we must use on Passover that has been used during the year for food, must be specially prepared for Passover. Some things can be cleaned for Passover, some cannot, as we shall learn, with Hashem’s help.
The Prohibition of eating chometz during Passover is no small matter. As we saw above, the Torah warns us that if we eat chometz during Passover his soul will be cut off from the Nation of Israel. This concept is rather complicated, but in essence it generally means being cut off from one’s spiritual source. It can also denote premature death and childlessness, depending on various concepts. (Now is not really the time to discuss what this means). The Torah is quite strict about this matter. We must therefore be careful not to eat even the slightest amount of chometz.
Passover is the favorite time of most Orthodox Jews. We work very hard to prepare for it, and that adds to the enjoyment, but in fact the Holiday itself is in many ways one of the most enjoyable Holidays of the year. Besides which, the Torah commands us to have joy on the Holidays, and Passover is very conducive to joy. Remember that both before and during Passover, and, as they say, Have a Happy and Kosher Passover!