This year (2011), Sukkot, also called Zman Simchateinu, (the time of our gladness), starts at sundown, Wednesday, October 12th, and lasts for seven days. Sukkot is immediately followed by two separate Yomim Tovim (holidays), Shemini Atzeret on Thursday, October 20th, and Simchat Torah on Friday, October 21st, but we commonly think of them as part of Sukkot.
In Eretz Israel, The Yom Tov of Sukkot lasts for seven days followed by one separate Yom Tov, - Shemini Atzeret on Thursday, October 20th.
"Sukkot" means "booths" and refers to the temporary dwellings that HaShem commands us to live in during this Yom Tov ( see Vayikra, Parshat Emor 23:42-43) as our ancestors, the Bnei Yisroel wandered through the desert for forty years, living in temporary shelters.
The covering (roof) of the Sukkah, or the S'chach (literally, covering) must be a material that grew from the earth, was cut off from the earth, and not susceptible to Tumah (contamination). This includes tree branches, corn stalks, bamboo reeds, and sticks. But metals, leather, growing trees and foodstuffs are excluded. S'chach must be left loose, not bundled together or tied down. S'chach must be placed sparsely enough that rain can get in, and preferably sparsely enough that the stars can be seen, but not so sparsely that there is more sunlight than shade, and not more than ten inches open at any point. The covering must be put on last.
It is a Mitzvah (obligation), and of course, a lot of fun, decorating the Sukkah. A favorite decoration is drawings or charts of the Ushpizin (guests), the seven eminent biblical guests we invite to honor us by visiting our Sukkah. They are: Avraham, Yitzchok, Yaakov, Moshe, Aharon, Yosaif and David.
Others hang live fruit like apples and grapes from the S'chach. Bees like to visit the Sukkah too. Honor the Sukkah by bringing in your finest utensils, but never any pots and pans. A Sukkah must be treated with respect.
Learn more about Sukkot in the Torah Tots site