A good starting point to get a sense of Burning Man is to read through the page of Frequently Asked Questions, the Glossary, and the Timeline. Then, start browsing through the event archives. You might want to carve out some time in your day when you take that on, because there's a LOT of incredibly absorbing and inspiring material to go through there.
Want to get a quick sense of what it's like to be at Burning Man? For a brief yet eloquent overview of the entire event from arrival to exodus, please read Molly Steenson's essay “What is Burning Man?”.
The event takes place on an ancient lakebed, known as the playa. Over 60,000 people make the journey to the Black Rock Desert for one week out of the year to be part of an experimental community, which challenges its members to express themselves and rely on themselves to a degree that is not normally encountered in one's day-to-day life. The result of this experiment is Black Rock City, home to the Burning Man event.
Art is an integral part of this experience, and in fact, is such a part of the experience that Larry Harvey, founder of Burning Man, creates an art theme each year, to help tie each individual's contribution together in a meaningful way. Participants are encouraged to find a way to help make the theme come alive, whether it is through a large-scale art installation, a theme camp, gifts brought to be given to other individuals, costumes, or any other medium that one may conceive.
By the time the event is completed and the volunteers leave, sometimes nearly a month after the event has ended, there will be no trace of the city that was, for a short time, the most populous town in the entire county.