You must be an annual passholder or a Florida resident to be eligible for TIW. That said, a year's membership (13 months) costs $75 for AP holders and $100 for Florida residents who are not AP holders. The card, when presented at a participating restaurant, is good for 20% off the full bill, including alcohol, for up to 10 people on the same bill.
It's good at most Disney TS restaurants but only 9 CS restaurants (most of those are at resorts - the only park where CS restaurants accept TIW is Animal Kingdom). There are 8 TIW blackout dates yearly, most of them over major holidays. An automatic gratuity of 18% is charged on all TIW checks at table service restaurants and bars/lounges, regardless of party size.