Contra dance is a kind of social dance with live music where a caller teaches the figures. You don't need to come with a partner, and while there is a short lesson before each of our dances it's optional. Most people learn contra dancing by doing it.
It looks like: http://www.youtube.com/watch?v=beOFeIIk4KY
You should wear comfortable clothes that you can move easily in. High heels don't work well. We'll have water but if you'd like to save cups bringing a water bottle is good.