The parks are probably the reason that you are going to Walt Disney World.  Your park tickets are what you will need to enjoy the four main theme parks or the Water Parks and More options.  A few years ago, Disney restructured their tickets so that everyone must buy at least a "Base" ticket, but they can add additional options to their tickets to gain more benefits.

1. Base Ticket – Provides admission to one, and only one park per day. Please note, even if you have an extra day on your base ticket you can not use it to visit a second park in a single day. This is the lowest priced ticket.
   
2. Park Hopper Option – Purchasing this option allows you to visit as many parks as you would like each day. This is worthwhile if, like us, you start in one park and maybe want to visit Epcot for dinner and Illuminations or if you stay in the first park until it gets busy and just want to go to another for the rest of the day. As usual a word of caution, if you have a 7 day or 10 day ticket it costs a certain amount (approx $56) to add it to the entire ticket but even if you only want to add it to one day the cost is the same – not good!!
   
3. Water Park and More Option – If you purchase this option it gives you a number of single day admissions (based on the length of your ticket) to the minor parks such as the water parks, Disney Quest, Wide World of Sports, etc. Pricing is identical to the Park Hopper Option and the number of the 1 day admissions you receive matches the number of days on your ticket. Unless you are sure you will be visiting the minor parks at least 2 or 3 times during your visit don’t get this option.
   
4. Premium Option – Combines all three of the above but does not include a discount for purchasing it.
   
5. No Expiration Option – This is the most expensive option and at least to us, doesn’t appear to be worthwhile. This option does, however, work for some folks but the biggest complaint I have heard is that the tickets have a way of getting misplaced and/or are forgotten and never used.