React JS Router is a library that enables navigation between different components in a React application. It provides a component to manage the routing functionality. Components can be rendered conditionally based on the current URL using components, which define paths and corresponding components. Navigation between routes is achieved using components, which generate anchor tags. Components used with React Router include BrowserRouter, Route, Switch, Link, and NavLink. These components facilitate the creation of single-page applications with multiple views, enabling seamless navigation and rendering of different components based on URL changes.