The save the date is a pretty thick packet that basically tells your guest that someone they know is having a fairy tale wedding so they may as well have a fairy tale vacation. The whole packet is all about planning a disney vacation. In the very back there's a pocket where they put the actual save the date.
It tell's your guests the date, the location, which hotels you've selected for them, and your website address. (I think you can personalize it more but I'm not sure.)