How to make very interactive animated website

So I've been looking at some o fthese insane website and was curious how to build these. I'm familiar with HTML, JS, React, but I have no idea how to build anything like that. These are the examples of the cool website that i have found and wanted to learn how to make

http://ift.tt/2j4ZTpA

http://ift.tt/2hVGkfN