Here are the steps to write a "Hello World" program in React:

1. Create a new React project using a tool such as Create React App.

2. Open the project in a text editor.

3. In the src folder, create a new file named App.js.

4. Add the following code to the App.js file:

import React from 'react';

function App() {
  return <h1>Hello World</h1>;
}

export default App;

1. In the src folder, open the index.js file and replace its content with the following code:

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';

ReactDOM.render(<App />, document.getElementById('root'));

1. Open the public/index.html file and make sure it has a div with an id of root.

<div id="root"></div>

1. Start the development server by running npm start in the terminal.

2. Open a web browser and go to http://localhost:3000/ to see the "Hello World" message displayed on the page.

And that's it! You have successfully written your first React program. You can now build upon this foundation to create more complex React applications.