Contra dance is rather like English barn dancing on speed. You'll recognise a lot of the terms, like stars, circles and ladies chains. Historically contra came to England from New England in the 1950's. The style has changed enormously during the passage across the Atlantic and back.
Every dance is explained first.
While you dance the caller will keep calling until people have the idea and will then shut up and let you dance. Normally people change partners after each dance, so you end up dancing with lots of different people. And we use live music, to keep the excitement up. Dances start in two long lines, usually everyone facing their partner. Each couple interacts with another couple, forming tight patterns, often with all the dancers moving at the same time.