Read all of the terms and conditions of the airline voucher in your possession before you attempt to use it. Many airlines list numerous restrictions for usage on their vouchers.
Look for a flight that you would like to take online or via a travel agent. Depending upon the terms and conditions of the airline voucher, you will likely need to fly with the same airline that issued the voucher.
Start booking your chosen flight online or via a travel agent. If booking your flight online, you may need to call the customer service telephone line to redeem the airline voucher.
Relay the details issued with your flight voucher to the customer representative when making the payment for your flight. For example, an airline voucher is usually issued by a specific airline to a specific person and has a reference number.