MEAN Stack has all technologies based in JavaScript. So if you don't know JavaScript, you need to learn and get very good at JavaScript. After that learning MEAN stack is about learning all the core technologies that are a part of the MEAN stack such as MongoDB, Angular etc. These technologies are quite intimidating to get started with. one thing that can make it easy is that they all use the same language which is JavaScript. So if you wish to learn MEAN stack you should learn each individual technologies first and then learn how to combine them to build web apps.
You can read this blog that explains what MEAN stack is.
To learn full-stack development from experts, enroll in this Full Stack Web Developer Course offered by Intellipaat.
You can also get started with MEAN stack by learning individual technologies, like:
If you wish to learn MongoDB you can do this end to end certification course on MongoDB.
Also you can learn Angular by doing this Angular course.