how to use simple script in react js code example

Example 1: link react to html

<script crossorigin src="https://unpkg.com/react@17/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"></script>

Example 2: react quick tutorial

ReactDOM.render(  
    <Hello />,   
    document.getElementById("root")  
);