What should I know to build this animation (link below)

First, you need to already know HTML, CSS and JavaScript.

Second, you can visit the Useful Links page to find an intro to three.js tutorial. Make sure you learn all the basics of scene, geometry, materials and animation.

Third, if you want to create your own 3D assets, you should learn to use Blender. Otherwise, you can import pre-existing assets that someone else made.