When you use require with relative paths in Node.js, you tell Node.js exactly where to find your custom modules. Always start a relative path with ./ for the current directory or ../ to move up one directory. This makes your code clear and avoids accidental conflicts with built-in modules or installed packages.

Folder structure.

project/
│
├── app.js
├── utils.js
└── helpers/
    └── math.js

You should avoid omitting the ./ or ../ when requiring your own files. If you write require('utils') instead of require('./utils'), Node.js will look for a core module or a package in node_modules, not your file. This can lead to errors that are hard to debug.

Keep your project structure organized and use clear, explicit relative paths. If your project grows, consider using absolute paths with tools like path.join or setting up module aliasing, but always be consistent and double-check your paths when moving files around. Remember, relative paths are resolved from the file where require is called, not from where you run your script.