Express.js is a light-weight Node.js web application framework that helps in organizing your web application into an MVC architecture on the server side.
It allows much better code organization and the access to several useful and powerful features without having to re-invent the wheel.
Express.js allows easier routing and usage of any templating solution with minimal effort.
It is very easy to learn and will save you a lot of time.
Learn more from the official website http://expressjs.com/