Don't worry it took me ages to get my head round this too
Basically you buy a voucher, as Small World says, for every member of your party for every night you are staying onsite.
Currently the standard vouchers are £13 for adults and £6 for children, though the prices are increasing soon. You have a list of restaurants where you can eat using these vouchers without paying anything extra. These restaurants will offer you either a set menu, or an eat-as-much-as-you-like buffet. As an example, you could take your £13 voucher to Annettes, and have a 19.99 euro set menu, or take it to the Cheyenne and have their buffet, normally worth 22 euros, all using your £13 voucher and not paying a penny more. If you hated the set menu you could ask to use your voucher at face value, at the moment face value would be worth 19 euros. You could then buy anything from the normal restaurant menu up to 19 euros, or more if you are willing to pay the difference. So with the current exchange rate as bad as it is, they do offer excellent value.
There are also half-board plus, and half-board premium vouchers. You pay more for these (see the sticky as I'm not sure of their current cost), they give you a greater range of restaurants to eat in, including some of the character restaurants, and although you would have a bigger outlay, the potential savings are higher than if you bought the standard ones.
We used these vouchers for the first time a couple of weeks ago and thought they were an excellent buy. like lots of others on here, i would highly recommend investing in them. As to which type you buy, it depends on the type of dining experience you want. I can highly recommend Annettes and the Silver Spur which were both on the standard vouchers list, and if you look at the restaurant sticky there are loads of great reviews to help you make you mind up (or give you even more indecision
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Hope that helps!
Could someone please explain it slowly and simply to me!!!!!!!!! 
