React (A JavaScript) Framework for your Front End Development

React is a JavaScript Library or Framework used for designing a website or web Application's User Interfaces also called frontend. React is developed and maintained by Facebook.

React code is made of entities called components. Components can be rendered to a particular element in the DOM using the React DOM library. When rendering a component, one can pass in values that are known as "Props"

React can be used as a base in the development of single-page or mobile applications. Now maybe you thinking; how it is made on a single page. This is where the actual use of React comes into practice. Why single page? because it makes your app faster. No need to load resources load every time when navigating to different pages. 

From this image you can you can understand pretty much

Explanation

There is only a Single HTML file consists a Div (an HTML tag) with id 'root'. This is where all the React Components Rendered.