There are two ways into React 7,897 . You can drop three lines into an HTML file and have a working component in a minute, which suits trying an idea or adding one interactive widget to a page that is otherwise server-rendered. Or you can scaffold a project with a build tool, which is what every real application uses: JSX compiled ahead of time, hot module replacement while you edit, and a minified bundle at the end.
This section walks both paths, then explains the files a scaffolded project gives you, the frameworks that sit a level above, and the two tools you will keep open all chapter.