A sukkah is a sort of tent. The plural for sukkah is "sukkot." Sukkot is also the name of a Jewish holiday which commemorates the time that the ancient Israelites wandered in the desert, sleeping in... none other than... sukkot!
And exactly why were they wandering in the desert? Well, they had just fled from being slaves in ancient Eygpt, where Moses, the leader of the Israelites, convinced Pharoah (after a number of very disturbing plagues) to "let my people go."
Once in the desert (Sinai) they slept and ate in temporary tents, or sukkot.
Pictured here is a my nephew Jackson is a minature sukkah I built for him.
Note that there is no fully covered roof on the sukkah... only branches. This is to remind people inside of the sukkah, as they look up and gaze at the stars, not only of the temporary outside shelters of their ancient ancestors, but also that life itself is temporary. Therefore, we should be thankful and joyful for all of our blessings.