This document is a work in progress and may never be really complete. This is a reflection of how I think about learning React, and may be wildly different from your approach, and that’s okay.
React is a library by Facebook for building user interfaces.
The library itself includes a rather straight-forward API. How you use that API is a question that has a number of answers, and there is a growing ecosystem of tools to use with React.
There is a “quick start” walkthrough on the official React website which tells the basics of the component API.