Check out the DC sticky in this forum. Lots of good info.
You will book your DC day either as "resort only" or including the dolphin swim. The time of your swim is assigned at check-in. You can book some people just the resort if they don't plan on doing the dolphin swim. You can also watch (and take photos) from the beach if only some members of your party are doing it.
All food is included for the day - breakfast, lunch, snacks, and drinks, including alcohol & icees.
The shark swim and Sea venture are separately priced add-ons for your day. Although in the grand reef, you can swim right up to the shark area and it feels like you are swimming with them. It's a very neat area to enjoy at no extra cost.
Also, if it would work in your plans, you can add on 14 days admission to Sea World & Aquatica for a nominal cost, as well as Busch Gardens in Tampa for marginally more.