It's the website for the School of Llama event. The event is already over though:
"Complete in-game tasks from the School of Llama website from today (Feb. 7) through March 7, 2023, at 11:59 PM ET. As you progress through the school’s paths, you’ll unlock in-game rewards."
Here is the official article for the full event details if you want to see it:
https://www.fortnite.com/news/fortnite-school-of-llama-commence-training-for-in-game-rewards
