Sukkot is a Jewish holiday which takes place in the Hebrew month of Tishrei. The start of Sukkot is generally in September or October on the Gregorian calendar. The holiday is celebrated for seven days at the end of which is the holiday of Shimini Atzeret which lasts for one day in Israel and two days outside Israel. The main aspect of sukkot are living in a tent-like structure called a "sukkah" (the plural of sukkah is sukkot which gives rise to the holiday's name).
A sukkah is tent-like structure. The details as to what constitutes a sukkah are not described in detail in the Bible but are discussed in the eponymous tractate of Talmud. The roof of a sukkah must be made from plant matter that has not been substantially altered. Jews often build sukkot after Yom Kippur but before the holiday of Sukkot has begun. Traditionally, the main obligations are to eat and sleep in the sukka. This is based on the Biblical passage in Leviticus 23:42 to dwell in a sukka for seven days.
The holiday of Sukkot has a variety of other aspects.
The Four Species
During the holiday four special plants (known as The Four Species) are taken together and waved in a ritual fashion. The four species are composed of the fruit of a citron, leaves from a willow, leaves from a myrtle, and a section of a date palm. The Four Species are often called collectively by either just the Hebrew word for the date palm (a Lulav) or together with the term for the citron (which is called an Etrog).
The first day
The Bible prohibits work on the first day of Sukkot. For historical reasons, this is extended to the first two days outside Israel. This prohibition is most relevant to Conservative and Orthodox Jews but not the other movements in that keeping the traditional work prohibitions is much less common among them. There are also associated liturgical differences that are correspondingly only apply to the first day in Israel and to the first two days outside Israel. Reform Jews outside Israel.
In ancient times, when the Temple stood, many sacrifices were offered on Sukkot. Traditionally, seventy sacrifices were offered to correspond to the seventy nations of the world. In Orthodox Jews and some Conservative Jews remember these sacrifices by reciting the Biblical section in Numbers which detail the sacrifices.