• Contrast React Router's approach to routing with routing we have seen in express
• Use npm to add react-router-dom
• Install and use React Router to manage routing in a React app
• Use React Router's navigational components: Router, Route, Link, NavLink, and Switch

Keep in mind that React Router went through a fundamental design change with the creation of React Router v4. There is lots of pre-v4 documentation and tutorials around so when researching/reading about React Router, be sure you are reading about the correct version.

• Official Docs: Many great examples and comprehensive. Assumes knowledge of other routing and comfort with React.
• CSS Tricks: React Router v4
• A Simple React Router v4 Tutorial on Medium
• React Router Introduction: YouTube video by the creators of React Router
• Routing with React Router v4 egghead.io (first couple videos)