index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
   <div id="root">

   </div>
</body>

<script crossorigin src="https://unpkg.com/react@18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.development.js"></script>
<script>

    // createElement returns an object . The parameters are name of the tag , attributes and children. The object is used by render to paint the DOM with attributes
    const parent = React.createElement("div",{id:"parent"},
    React.createElement("div",{id:"child"},
    [React.createElement("h1",{},"I am a h1 tag"),React.createElement("h2",{},"I am a h2 tag")]))


    const root = ReactDOM.createRoot(document.getElementById("root"))

    root.render(parent)
</script>
</html>