The "Park Hopper Option" on park tickets allows guests to come and go between the different parks. It is an option we have always enjoyed because if one park gets too crowded, we "hop" over to another one. It is explained
here as well. I do know some guests are very happy beginning their day and ending their day at one park because it is less complicated and saves money.
The "Waterpark fun and more option" allows you to visit additional attractions at Walt Disney World such as
Blizzard Beach,
Typhoon Lagoon, Disneyquest,
ESPN Wide World of Sports, or a round of golf at
Disney's Oak Trail Golf Course. If any of these are of interest to you, the addition on your ticket will let you do those things. If you are traveling in the colder months, you may not be able to visit the water parks. Our experience when we first visited Walt Disney World is that we found we had plenty to do just at the four parks, so we didn't visit the water parks until many trips later. However, many guests do like to break up their days at the parks by relaxing in the water or immersing themselves at the interactive games at Disneyquest (which gets you out of the Florida heat!).
Thanks for the question. If we can help you as you continue to plan your first trip, please don't hesitate to ask more questions.