Wanna Get Away fares are non-refundable so you get a credit good for a future flight. You must travel within one year of the date you booked the original flight. Example: You book a flight today (12/23/2016) for travel in May 2017. In March 2017, the price of your flight drops so you use the "Change Flight" option on Southwest's website to reprice your flight. You now have a credit for the difference that can be applied to the price of a flight that departs no later than 12/23/2017 (or maybe 12/22/2017).
The credit is tied to the original passenger so if you reprice your flight and get a credit, the Travel Funds that you get back can only be applied towards another ticket for you. To use those funds when purchasing another ticket, you enter the confirmation number of the flight that generated those funds so save that original confirmation number when you reprice a flight.