I'm trying to make an countdown website for a project. I want that the countdown is triggered by a button. I'm using React but i keep getting this error

React Hook "useEffect" is called in function "countdown" that is neither a React function component nor a custom React Hook function. React component names must start with an uppercase letter

I'm pretty new to react, can somebody give me some advice to fix the problem ?

the code:

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

function App() {
  const time = 20;
  const [count, setCount] = useState(time);

  const startCount = () => {
    useEffect(() => {
      if (count > 0) {
        setTimeout(() => setCount(count - 1), 1000);
      } else {
        setCount('Times up');
      }
    });
  };

  return (
    

      
{count}
       start 
       pauze 
    
  );
}

export default App;