-------- Heading.jsx page -------------

import React from "react";
import ReactDOM from "react-dom";

function Heading(){
  return <h1>This is My Componente Heading</h1>
}

export default Heading;

---------  main page ----------

import ReactDOM from "react-dom";
import Heading from "./Heading.jsx"; // is optional the .jsx
import Ulist from "./Ulist";

ReactDOM.render(
  <div>
    <Heading />
    <Ulist />
  </div>,
  document.getElementById("root")
);