index.jsfile in any folder under pages folder will work as a landing page for that folder
A simple About.js file under folder pages is equal to the index.js file under About folder under Pages folder.
Both can be accessed through domain.com/About
You will often see the file name like [abcd].js it is valid , if the domain.com/something does not exist
then , this file will be accessed automatically.
There is a file name convention like [...slug].js , if the user types any imaginary file path like
domin.com/anything/he/want then this file will be accessed and it will show
{slug : ["anything" , 'he' , 'want']}
when running console.log(router.query) --------> import {router} from "next/router"