An advent calendar is used from Dec.1st to 25th. You make it ahead of time and put a small piece of candy or a coin in the pocket. Everyday, whomever you made it for, takes the candy to eat or the coin to put in a piggy bank. It helps children count the days until Christmas morning.
http://www.fabricfreedom.co.uk/QuiltsAndProjects.html
Scroll about 1/2 way down and there are free instructions