HP Approaching the Wizarding World

Why did the unicorn die tragically in the forbidden forest? Why did the teachers change so frequently? Whose name is it that people don't dare to say? What secrets are hidden under the halo of the savior? Explore the essence of magic, pursue the origin of the world, let us approach the magic world of HP. (Harry Potter fanboy, daily life, the protagonist is passionate about studying magic, please clear the mines reasonably, thank you in advance.)