Hi there, Karlijn! Welcome to planDisney. It's always so exciting to plan a Walt Disney World adventure.
Once you are in the U.S.A. it is possible to buy a 1-day Standard Ticket (subject to availability), which provides entrance into one park for one day. All ticket prices are subject to change and vary by day. There are additional upgrades to purchase when you are Stateside, such as the Park Hopper Plus option, which is again subject to surge pricing.
Although these tickets can be purchased at the Main Entrance Ticket Booth, I recommend buying tickets in the States online, or by calling U.S. Guest Services, just so there is no availability disappointment at the door.
Karlijn, did you know that you can book
2-day tickets from home? You might like to check these out if you would like less work to complete while in Florida. Some options include
Park Hopper, which means you could see even more of the magic Walt Disney World offers. As you are planning to visit in June, you'll be able to see all the blossoms and topiaries on offer at
EPCOT's Flower & Garden Festival. You can also delight in all the delicious delicacies prepared by the Outdoor Kitchens.
I wish you blue skies and sunshine for your adventure in the Most Magical Place on Earth, Karlijn. Please let me know if you need anything further, Louise.