Using React Router v4 with create-react-app - https://codingblast.com/react-router-create-react-app/

App.jsx

import React from 'react';
import './App.css';

import { BrowserRouter as Router, Route } from 'react-router-dom';

const Home = () => <h1>Home</h1>;
const Admin = () => <h1>Admin</h1>;

const App = () => (
  <div className="App">
    <header className="App-header">
      <Router>
        <div>
          <Route path="/" component={Home} />
          <Route path="/admin" component={Admin} />
        </div>
      </Router>
    </header>
    <p className="App-intro">
      To get started, edit <code>src/App.js</code> and save to reload.
    </p>
  </div>
);

export default App;