en passant

As I have never read a book or studied the game of chess, anything Ive picked up is by playing on this site. Anyway, the one thing that still confuses me is en passant. What are the rules, or how and when can this be done?

Originally posted by 29inchlegs
As I have never read a book or studied the game of chess, anything Ive picked up is by playing on this site. Anyway, the one thing that still confuses me is en passant. What are the rules, or how and when can this be done?

cheers for that