React calls few functions in a certain order. render() is a lifecylce method after which componentDidMount() and other functions are called. You can make your ajax or async request inside this componentDidMount method. From this point you could check the official docsto learn more about Reactjs. So far what we have seen is for learning purpose. In actual development, we will use webpack and other tools (like create-react-app, next.js, gatsbyjs) to organize components and build.

If you want to update this tutorial, you could give a PR to this github repo