You need to have a package booked through Disney, but not necessarily at one of their 3 hotels, you can be at a Good Neighbor Hotel. It is NOT like the dining plans at WDW, which while they are no longer the fantastic value they used to be, are still generally a pretty decent value. With the DL dining plans, you are getting vouchers. You buy the plan in I think 2-5 day increments, which do not have to match the number of nights you are staying or the number of days tickets you have. A typical day is one character meal voucher, one $15 voucher, and one $5 snack voucher. If for some reason what you purchase is less than $15, you will not get a refund, and if what you choose comes to more than $15, you are paying the difference. I suppose it is possible to break even on what you paid for the plan versus the dollar value of the food you buy, but it's not a guarantee, and I don't think you are really saving money, if anything maybe prepaying your vacation. I think it's probably better to just put money on a Disney GC if you want to prepay your trip, that way you are less likely to lose money. You can go to the DL site and get the prices for the different plans, and it will show you just what they include. My information is from memory!
okay, just looked at DL site....2 day plan is $106 per adult and includes 2 character meals, 2 $15 vouchers, and 2 snack vouchers. It does not say the value of the snack voucher, but from memory a few years ago, it was $5, it might be a bit more now. You can also purchase just character meal vouchers without a plan, and with them they make a distinction between regular and premiere character dining, the premiere is Goofy's Kitchen and the princess meal at Ariel's, not sure if the vouchers that come with the dining plan could be used for those, if so, that would make them a better value. To check out prices, just go to the DL site like you are booking a trip, put dates in, number of people and then once it brings up the hotels, click on view/edit details and it will show you the different components of the dining plan, click on each to see the prices and what exactly is included.