The Jewish festival of Passover or Pesach is celebrated for eight days by most of the Jewish people who live outside of Israel - except for most Reform Jews, most Reconstructionist Jews and some Conservative Jews who celebrate Passover for 7 days - and will commence in 2016 either just after sunset or just after nightfall - depending on which rabbinical opinion that one follows - on Friday, April 22nd, 2016. Furthermore, for both a Jewish festival and Shabbat/the Sabbath, due to their holiness, there is a custom to “extend” the time frame for both a Jewish festival and Shabbat/the Sabbath by “borrowing” time from the day previous to and the day following either a Jewish festival or Shabbat/the Sabbath, respectively. The time “borrowed” from the previous day can be anywhere from 15 minutes to a half-hour depending on the rabbinical opinion one follows. The time “borrowed” from the day following either a Jewish festival or Shabbat/the Sabbath can be anywhere up to a half-hour depending on the rabbinical opinion one follows. Therefore, for those that follow this custom, this means that the Passover festival will begin anywhere from 15 minutes to a half-hour before sunset or nightfall. The most popular time for starting both a Jewish festival (as well as Shabbat/the Sabbath) is at 18 minutes before sunset so for many Jewish people, this is when the Passover festival will begin in 2016. Since in 2016 the first day of Passover falls on Shabbat, then both Shabbat and the first day of Passover will begin for most Jewish people at 18 minutes before sunset or at whichever extended time before sunset one customarily begins a Jewish festival and/or Shabbat for those that extend their time. Similarily, those that extend the time for Shabbat and/or a Jewish festival will end both the holiday and festival anywhere up to a half-hour after either sunset or nightfall depending the custom they follow.
Passover will conclude either at sunset or at nightfall - depending on which rabbinical opinion that one follows - on Saturday, April 30th, 2016, or in the Hebrew/Jewish calendar, from 15 Nissan 5776 to 22 Nissan 5776, for Jewish people who celebrate the Passover or Pesach festival for eight days (some Reform Jews, some Reconstructionist Jews, and most Conservative Jews, in addition to Jews living outside Israel). For Jewish people who celebrate the Passover or Pesach festival for seven days (as I mentioned, most Reform Jews, most Reconstructionist Jews and some Conservative Jews, in addition to Jews living in Israel), the Passover or Pesach festival will conclude either at sunset or at nightfall on Friday, April 29th, 2016, or in the Hebrew/Jewish calendar, from 15 Nissan 5776 to 21 Nissan 5776. If one follows the custom to “extend” the day for a Jewish festival, the ending time for Passover for those who celebrate Passover for seven or eight days can be anywhere up to a half-hour after sunset or nightfall depending on the rabbinical opinion one follows.
The first two days and the last two days of the festival for Jews who celebrate Passover for eight days are considered "full" holy days ("Yom Tov" days in Hebrew), meaning the full application of Jewish law ("Halakhah" in Hebrew) apply to those days, which include a prohibition against performing work unrelated to the Pesach/Passover festival; therefore, Jews who choose to follow Halakhah do not work on these days. For Jews who celebrate Passover for seven days, the first day and the last day of Passover are Yom Tov days.
Yom Tov days are full holy-days or holidays (in the case of Passover, Yom Tov days are "full" festival days, meaning the full application of Jewish law for Passover apply to those days), and so Jewish people are instructed by Jewish law to devote their energies to prayer and full observance of the Passover festival. The intermediate days of Passover are known in Hebrew as "Chol HaMoed" days. "Chol" or "Hol" means "Weekday" in Hebrew and "Moed" means "holiday" or "festival" in Hebrew. Taken together, "Chol HaMoed" means "The Weekday Holiday" or "The Weekday Festival" in Hebrew. On these days, according to Jewish law, Jewish people are permitted to work unless the work falls under the 39 forms of forbidden work during Chol HaMoed days. However, Jewish people are still required to observe the appropriate prayers for the Passover festival during Chol HaMoed days, so for these reasons Chol HaMoed days have been referred to as "Half-Holy-Days" or "Half-Holidays". For Jews who celebrate Passover for eight days, Chol HaMoed days include the 3rd, 4th, 5th, and 6th days of the Passover festival. For Jews who celebrate Passover for seven days, Chol HaMoed days include the 2nd, 3rd, 4th, 5th, and 6th days of the Passover festival.
Passover celebrates the physical and political freedom of the Hebrews following their departure from Egypt. However, the Hebrews would only attain their spiritual freedom 50 days later when they received the Torah and its 613 commandments at Mount Sinai. With their physical, political, and spiritual freedom achieved, the Hebrews had gained the foundation for reaching greater heights as human beings when they finally reached and entered the Land of Canaan. In order to celebrate Passover according to the laws of Halakhah (Jewish law), two special commandments ("mitzvot" in Hebrew) are fulfilled. The first mitzvah is to eat only Matzot, unleavened bread, for the eight days (seven days in Israel) of Passover. The house is cleaned of all bread, cakes, and products that are leavened and/or made with leavening agents such as yeast. Only products affixed with a label from a reliable kashrut organization, council, or qualified individual that reads - either in English, Hebrew, or the language of the country under the jurisdiction of the kashrut organization, council, or qualified individual - "Kosher for Passover" or "Kosher For Pesach" are purchased and used for the eight days (seven days in Israel) of Passover.
The second Mitzvah is called "Haggadah", which means "telling". One is commanded to tell and retell the story of the Exodus from Egypt on the first evening and second evening of Passover (for Jews who celebrate Passover for eight days; for Jews who celebrate Passover for seven days, only the first evening applies). The Haggadah is read at the Seder, which is a special meal that takes place on the first and second evenings of Passover. For Jews who live in Israel, the Seder meal only occurs on the first evening of Passover.
The mitzvah of Haggadah is mentioned four times in the Torah using the words: "And you shall tell it to your children on that day." The four times that the mitzvah is mentioned is the source for the "Four Questions" (the "Ma Nishtana", meaning the "Four Questions" in Hebrew) and the source for the parable about the "Four Sons", which are both part of the reading of the Haggadah at the Passover Seder meal.
I, personally, find it fascinating that the emphasis on Passover for remembering one's freedom as a Jew is through the action of transmitting one's heritage by teaching, and explaining to one's children, what it means to be a free person. It shows me that the essential part of one's heritage is based on the family and the passing on of one's traditions from one generation to the next.