Here's an example of how MEAN can be used to build a simple web application. Let's say we want to build a todo list application. We would start by creating a MongoDB database to store our todo items. We would then use Express.js to create a RESTful API that allows us to create, read, update, and delete todo items from the database. Next, we would use AngularJS to create a user interface that allows users to interact with the API and display the todo items. Finally, we would use Node.js to run the application on a server.