React is Facebook’s component-based web development framework for making UIs and offering declarative views, which makes the code more predictable and easier to debug. It does not support controllers or models. React can also render on the server using Node and power mobile apps using React Native. In short, it allows you to build powerful, fast, user-friendly and reactive web apps. If you want to learn React then React 16.6 — The Complete Guide is a good course to start with. You can take this online course on Udemy.