First, we have to know that those stacks are Full stacks so you do the Frontend and the Backend.
It's a programming (scripting) language used both on the client-side and server-side that allows you to make web pages interactive.
Express.js: It is a back end web application framework for Node. It is designed for building web applications and APIs.
MongoDB: It's noSQL (Json-like) database .
In those stacks there are common letters which are M - E - N .
- M: MongoDB
- E: Express.js
- N: Node.js
Those are the Backend technologies be while the Frontend technologies are A - R - V for MEAN - MERN - MEVN .
- A: Angular
- R: React
- V: Vue
So, choose the stack that you love but before you have to learn the basics if web development which are:
- JS Dom and Bom
- ES6 Syntax
- SASS (optional but preferred)
- CSS Frameworks ( Bootstrap, Tailwind CSS, etc...)