(I am committed this year to doing a post before every holiday, and unfortunately all I can think of is an explanation of holiday customs.)
Sukkot is one of the two holidays on which Jews remember the literal or metaphorical (depending on whom you ask) experiences in the desert. It is also a harvest festival. On Sukkot, Jews build a booth called a Sukkah to represent the temporary housing used in the desert and during the harvest season. Observant Jews eat all meals in the Sukkah for the duration of the holiday (seven days), and some even sleep in the Sukkah.
Even though the holiday is seven days long, only the first two and the last one are known as "Chag" (Ch=clear your throat) when work is forbidden. For the rest of the week, celebrations continue, but work may be done.
The other big part of Sukkot is the lulav and etrog. These are three species of plant and one fruit that are held together and waved in all six directions to tell us that God is everywhere.
Special extra prayers in praise of God are also said during Sukkot.