• Class = ClassName

  funtion APP(){
  	<div className="APP">
  </div>
  }
  

• src > components > test.js

import logo from './logo.svg';
import './App.css';
import Test from './Test';
import React, { useEffect, useState } from 'react';

function App() {
  const [count, setCount] = useState(0);

  console.log(count);
  
  return (
    <div className="App">
      <div>{count}</div>
      <button onClick={() => setCount(count + 1)}>Click</button>
      <Test/>
    </div>
  );
}

export default App;