As Gary posted, you have one year from the date you BOOKED the original flight to travel using those funds. Example: if you made a reservation on March 1, 2017 for a flight later this year and then you cancel that flight, you can use the funds for a trip that takes place no later than March 1, 2018 (or maybe Feb 28, 2018?). The funds can only be used by the original passenger.
Keep track of the confirmation number of the cancelled flight. You need that to access the Travel Funds that you get from the cancellation.