Over the years, Disney has offered different iterations of its FastPass system, where guests can enter shorter lines at a number of attractions.
Although it was temporarily suspended during the coronavirus pandemic, the most recent iteration required that passes be scheduled in advance using the My Disney Experience app or kiosks around the parks.
At the start of any day at the parks, you could schedule three FastPasses, but you had to use all of them before you can make more.
To optimize your time, it's best to schedule all three early in the day so there's a chance you can make more. It's also a good idea to look at your meal reservations and general plans for the day so you're not constantly rushing from one side of the park to the other to catch a FastPass window.