ISO help using File->New->Module

I would like to create a new module (at least I think I do) where I can put scala code which sees the existing code in my project, but where that visibility is one way.  The goal is that I can create broken code at one place, which fails to compile, but I can still compile the main code without burden.

When I use the File->New->Module menu item, I get a new directory which does not look at all like the Scala directory structure I'm expecting.    It does not have a `src/main/scala` nor `src/test` directory.    Am I responsible for creating all these directories myself?

Also how can I create Scala code in this newly created (sub) module which is able to import code in the main area, not in the submodule?