Hello Ruth,
Thanks for stopping by 
planDisney with your question. Whether you're heading to Walt Disney World next week or next year, it's exciting to start making plans for that next vacation!
Right now, in addition to purchasing park tickets, guests need to 
make a reservation for EACH day that they visit a Disney theme park. If you add the 
Park Hopper Option to your tickets, you still need to make a reservation to the FIRST park you plan to visit each day; however, as long as you've checked into the park that you reserved, then after 2:00 PM (or whenever park hopping begins), you can head to a second, third, or even fourth park without making an additional reservation. 
For example, if had a two day ticket with Park Hopper Option, I might make a reservation for my first day at 
Disney's Hollywood Studios and make a reservation for 
Disney's Animal Kingdom on my second day. My touring plan on the first day would start in Hollywood Studios with some of my favorite attractions:
 Star Wars: Rise of the Resistance, 
The Twilight Zone Tower of Terror, and 
Rock 'n' Roller Coaster Starring Aerosmith. I might make a lunch reservation at 
Beaches and Cream Soda Shop at Disney's Beach Club Resort and walk or take a boat there before strolling to 
EPCOT at 2:00 PM to enjoy that park and end my evening seeing 
Harmonious, my favorite nighttime show. 
My plan on day two would include an early morning entry to explore Disney's Animal Kingdom, making sure to experience 
Kilimanjaro Safaris and 
Avatar Flight of Passage. I would probably head back to my resort for a short rest after lunch and then head to 
Magic Kingdom to finish my trip with some classic attractions like 
Pirates of the Caribbean and end the night watching fireworks over Cinderella Castle during 
Disney Enchantment. I know I wouldn't be able to see and do everything, but I would be able to experience some magic from each park.
Hope this helps. Enjoy planning your next magical vacation!
Diane