Hi Jose Manuel! Welcome to planDisney!
I'm excited to hear that you're planning a visit to the 
Most Magical Place on Earth! Before you know it, you'll be arriving for an amazing stay filled with unforgettable experiences!
Jose Manuel, I see that you currently reside in Spain. Guests 
purchasing tickets on the EU-based website or while located in this country must purchase a minimum of a two-day park ticket. Single-day tickets will become available once you arrive in the United States for your stay. Upon arrival, you can access the US-based website to purchase an individual day ticket for the Magic Kingdom. The ticket should automatically link to your My Disney Experience account; otherwise, you can manually link it after your purchase. You'll need the confirmation code that will be sent to your email address to complete the process.
With some new additions to the 
Magic Kingdom, you'll have plenty of experiences to look forward to. Disney Starlight: Dream the Night Away recently debuted and has been a welcome addition to the nighttime entertainment. This is a new nighttime parade that includes dazzling lights and your favorite Disney characters. I grabbed a spot along Main Street U.S.A. on a recent visit and was incredibly impressed with each passing float that went by.
I hope you have a magical time during your stay, Jose Manuel! 
Stop back and see us again at planDisney!
Greg