At BarCamp, a group of enthusiastic people gather to share their knowledge about technology and anything else they are interested in. They do this by attending presentations given by other attendees - and giving presentations themselves, of course. A BarCamp presentation can be as formal or informal as you like. You can go to any session you like, and if you don’t find a session interesting, you can leave and go to another. Everyone is encouraged to give a session or participate in whatever way they can. When sessions aren’t running, there’s usually other fun stuff happening: food and drink, games, conversation, silliness, and people hacking on projects and building things. Don’t be afraid, there’s lots of good stuff going on at BarCamp.
BarCamp is a “participatory unconference”, so you, the attendees are going to be making the event as great as it can be. The idea is that everyone who comes takes part in some way: that might be running a session (which is not as scary as you might think), taking photos, blogging, tweeting etc.