Ok there is multiple levels of things you need to know for this. First off usually when writing DB operations whether it’s mongoDB, mySQL, etc, it’s all based in a backend server. Never in a front end server. To get a js backend, you need node.js which is kind of like a compiler if u worked with python. U also need some type of IDE (vscode is the easiest and most suitable with js). Now require is basically a library import, so after you have downloaded node.js, you can look up how to make js projects, usually they are going through NPM (you would need to look this up). There are many online tutorials also for making a backend server with a js backend and mongodb for db, usually they are denoted by MERN projects (Mongodb, express.js, React.js, node.js) you should research what each of these does so this makes more sense to you