When and where to use js modules? [closed]

I’ve read a little about them on https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules but I’m still a unsure how exactly I should be splitting up my code. I’ve got functions that attach event listeners, functions feed into said event listeners, and even a couple of fetch calls that add elements to the webpage.

Everything is currently in one js file but I would like to break it up for organization and loading efficiency but I want to avoid possibly adding unnecessary delay to page functionality.

Any advise on this? When to use modules, what should be in a module, places I can see examples of this?