But before that we need to make sure to have node.js and npm installed in the computer. Optionally we can use CRA(Create React App) which is a tool built by developers at Facebook to help you build React applications. It saves you from time-consuming setup and configuration. You simply run one command and create-react-app sets up the tools you need to start your React project.
The command line should give you an output where you can find the application in the browser. The default should be localhost:8080. If you are only using IE or Edge on your Windows machine, I can recommend you to install Chrome as well to access the developer environment and the React Developer Tools which are available as Chrome extension.
In the above, App.js is called a component. Normally, we make multiple components and put them together in App.js, which will then be rendered in index.js, and finally, into the root div in index.html.