New poster to FT, here and I don't know much but do have experience with WN. When you reach 16 points, they automatically mail a voucher to you. Mine came with free drink coupons. You have one year from issuance to use the voucher. I was told by the FA the drink coupons never expire. To use the voucher, book your flight, pay the taxes & fees (mine were $10) and present the voucher at check-in. Make sure you don't forget the voucher--you must present it or pay for the ticket upon check-in.