Official Intro - This tutorial doesn’t assume any existing React knowledge.
Introduction to the React by FreeCodeCamp - React, created by Facebook, is an open-source JavaScript library for building user interfaces. It is used to create components, handle state and props, utilize event listeners and certain life cycle methods to update data as it changes.
Other useful links
Intro to Redux - The only introduction to Redux (and React-Redux) you’ll ever need
All things React - Top 50 React Articles for the Past Year (v.2019)