Preparations

MongoDB

MongoDB is a leading NoSQL database that uses JSON-style documents with dynamic schemas. Go through this very short tutorial for MongoDB here. This 5 minute tutorial will help you understand how MongoDB works as a noSQL DB service. Even though MongoDB is fast, scalable and easy to use, to make it work with the MEAN stack, we need an object modeling service called Mongoose.
Skim through the Mongoose guide (getting started) here to get a sense of how it works.

Express

Express is a minimal and flexible node.js web application framework, providing a robust set of features for building single and multi-page, and hybrid web applications.

AngularJS

Go through the tutorial here.