I've never heard of a "tango card" until I've made my first payment request 3 years ago on inboxdollars.com. From what I've learn, a tango card's value is based off the earnings you receive from completing tasks on one of the many reward earning sites online. Once you've earned one, a code will be sent your email. From there, you can use it to choose any of the giftcards that's listed on it's site. When you've made your choice, just enter how much you want on your giftcard. What ever value you applied to your giftcard will be subtracted from your tango card's value.
Tango cards never expire, so if your tango card has any money left over, you can use that to get another gift card. If your diligent enough to do online surveys or many other tasks, you'll be able to earn a tango card of your own.