If you signed up with a GAD group (Habitat Homes, local animal shelter, etc.) and did your volunteer work than you would have been given a link to get your GAD voucher. The person named on the voucher can then turn their GAD voucher in to WDW for either a one day non-hopping ticket to be used the day you redeem the GAD voucher, a FastPass exchange card good for X number of FPs for certain rides, a little hat figurine with special trading pins or you can dontate the GAD ticket to certain non-profit organizations. Check out the Ticket sticky in the Theme Park section.
HTH