"The fifteenth day of the seventh month shall be the holiday of
Sukkos... The first day shall be a holy day." (Vayikra 23:34-35)
We are commanded to refrain from work (except for food preparation) on the
first day of Sukkos (two days in chutz la'aretz).
Sukkos is called "zeman simchaseinu," the time of our joy. It is
the culmination of the shalosh regalim, the three major holidays of
Pesach, Shavuos, and Sukkos, which correspond to the three avos.
This holiday brings us close to Hashem, as when we were in the desert
surrounded by the Clouds of Glory. The Clouds of Glory are commemorated
by the sukkos (booths) we dwell in on this holiday.