MEAN Stack has Four Main parts namely MongoDB as a database, Express as Web Framework, Angular JS as a Front-End Framework, Node JS as Server platform.
You can use MEAN generator and Yoeman(Web Scaffolding tool) to build MEAN application. It will create a initial repository and set up necessary libraries needed.
You can refer some online videos like https://thinkster.io/tutorials/mean-stack, youtube videos to get started initially. If you catch up stuff, then it will easy to you to build dynamic web applications.
You can refer this webpage, where you will understand more about MEAN Stack http://meanjs.org/docs.html#folder-structure
If you need any help or any clarification. Message me