stuck on Edit src/App.js and save to reload screen, React

im trying to use react, and I'm quite confused by what it says here. Im trying to open my 'localhost' but it say's this:

Edit src/App.js and save to reload

and I don't know what it means by that, can someone help me with this? I'm new to react. this is the code I have in visual studio code:

function App() {
  return
  (
  <div>
  <h1>Cats R Us</h1>
  </div>)
}

export default App;

Im trying to edit it, but it wont work. it's stuck on that screen. please help me, im trying to do a course.