Meaning of parentheses () in Next.js path

For example (auth):

I was struggling to how to find correct path when () in the folder. I took a project from GitHub. Can anyone explain me how can I handle that?

When using the app (as opposed to pages) router, parentheses around a directory name indicate route groups:

In the app directory, nested folders are normally mapped to URL paths. However, you can mark a folder as a Route Group to prevent the folder from being included in the route's URL path.

This allows you to organize your route segments and project files into logical groups without affecting the URL path structure.

...

A route group can be created by wrapping a folder's name in parenthesis: (folderName)

In your example the routes would be mapped to e.g. /create-password, not /auth/create-password.