The detailed commands and prohibitions:
- Tashbisu-The command to destroy Chametz:
The positive command for one to destroy his chametz begins to apply at midday of Erev Pesach.
- Baal Yiraeh and Baal Yimatzei-The negative command against owning Chametz:
The negative command against owning Chametz begins to apply on the night of the 15th.
- Prohibition of eating Chametz:
It is Biblically forbidden to eat Chametz beginning from midday of Erev Pesach. One who eats Chametz on Erev Pesach, past midday, receives Biblical Malkus. However the Kareis penalty for eating Chametz only begins at night.
- Prohibition against benefiting from Chametz:
It is Biblically forbidden to benefit from Chametz beginning from midday of Erev Pesach.
- Bedikas Chameitz:
There is a Rabbinical obligation which requires one to search for Chameitz in all his properties and then destroy it. Biblically, it suffices for one to merely disown the Chameitz prior to midday of Erev Pesach.
The prohibition of owning Chametz-“Baal Yiraeh Ubaal Yimatzei”:
Owning Chametz: The Torah forbids owning Chametz on Pesach. This applies even if the Chametz will not be within one’s home over Pesach, but will be left elsewhere, in an area that one owns. Likewise this applies even if the Chametz is hidden away in an area from which the Chametz is not visible. However this only applies to Chametz that is within ones property, either through ownership, rental, or borrowing. If however the Chametz is within an area that he does not own and he did not borrow, such as he placed the Chametz in public property or in the house of another person without his knowledge, then Biblically it may be left there over Pesach. However Rabbinically he is obligated to destroy the Chametz that he owns, even though it is not within his property.
Liability on Chametz: If one does not own the Chametz but has liability over the Chametz, such as if the Chametz were to be stolen one would have liability to pay for the loss, it is nevertheless Biblically forbidden to have such Chametz in one’s property over Pesach. It is however permitted to have such Chametz left in the gentile’s property.
Storing Chametz that one does not own: If one does not own the Chametz and does not contain liability over it, it is Biblically permitted to have the Chametz remain in one’s home over Pesach; although Rabbinically is forbidden in certain cases, as will be explained.
The following is derived from the verses:
Lo yeirahe…..bigvulcha: This verse teaches us that one cannot own Chametz and have it left in an area that one owns, even if the area is not in one’s house. This includes even an area which one has rented or borrowed. Thus if the Chametz was placed in someone else’s house for him to guard and he had that area where the Chametz is staying lent to him, it is Biblically forbidden to own this Chametz over Pesach.
Lo yiraeh Licha: This verse teaches us that that Chametz which is un-owned, or Chametz which is Hekdish, or Chametz that belongs to a gentile, may Biblically be left in one’s property over Pesach.
Lo Yimatzei: This verse teaches us that it is forbidden to own Chametz even if it is placed in an area which is out of sight. Thus one cannot hide the Chametz in his pit. The lack of the word “Lachem” by “Lo Yimatzeh” teaches us that even if a certain Chametz does not belong to a Jew, but he has liability over that Chametz, then if the Chametz is within his property, he is nevertheless Biblically forbidden in having this Chametz over Pesach.
Gvulcha/Bibateichem: This verse teaches us that Chametz which one owns or has liability over, is only forbidden to be left in property which one owns or has borrowed, however if it is not in ones property then it may be left there over Pesach.
When does Baal Yiraeh and Baal Yimatzeh begin to apply?
One only begins to transgress the commands of Baal Yiraeh and Baal Yimatzeah from the night of the 15th of Nissan and onwards, as the verse states “For seven days yeast shall not be found in your home,…and you shall not see yeast in all your property for seven days”. [Thus we learn from the verse that] prior to the 7 days, one does not transgress a negative command if he owned Chametz in his house.
Tashbisu-Destroying the Chametz from midday and onwards on Erev Pesach?
Although one does not transgress a negative command when owning Chametz prior to the night of the 15th, nevertheless, [he is Biblically obligated due to a positive command, to destroy all Chametz from his home] from midday of the 14th and onwards. If he did not destroy his Chametz [at that time], then he transgresses the positive command for every moment thereon.
The source to destroy on the 14th: This is learned from the verse “Seven days you shall eat matzos, although from the 1st day you should destroy [Tashbisu] the Chametz from your homes”. The oral Torah teaches that the “1st day” in this verse refers to the 14th of Nissan, and [when it] is called the first day of the seven days of Pesach, it means to say that it is prior to the seven days. Accordingly the verse intends to say that matzahs are to be eaten for the 7 days, [although] the Chametz is to already be destroyed the day before the seven days.
The proof to destroy from midday: A proof to this matter [and the fact that only from midday of the 14th must it be destroyed] is learned from the verse which says “You shall not slaughter over the Chametz the blood of the sacrifice”, which means to say that one may not slaughter the Pesach sacrifice while one still owns Chametz. Now, the time for the Pesach sacrifice [begins] from midday of the 14th and onwards, thus from this [above verse] you learn that the time for destroying the Chametz is at the time of the Pesach sacrifice, which is from midday of the 14th and onwards.
How does one fulfill the Mitzvah of Tashbisu-destroying the Chametz?
Biblically, destroying the Chametz [in fulfillment of the Mitzvah of Tashbisu] means that one eradicates [Mashbis] and destroys the Chametz completely from the world until no other person can benefit from it. [The specific methods are explained in 445].
 Rambam 1/8; Magid Mishneh ibid in name of Geodnim; Rosh; Tur
 440/1; 440/9
 431/2; 440/2
 431/2; 440/2
 440/1; 440/11
Does one who disowns his Chametz fulfill the Mitzvah of Tashbisu? Admur ibid implies that the nullification of Chametz does not fulfill the Mitzvah of Tashbisu. See also 445 for an extensive research on this topic as to whether the Mitzvha is a Kum Veaseh or is Sheiv Veal Taaseh.
Other opinions: The Rambam [Hilchos Chametz Umatzah chapter 2 Halacha 2] rules that the destruction is done by nullifying the Chametz in ones heart.