Creating a displayable ‘index’ of content nodes within a path

Ok, it’s been over a decade since I’ve worked with Drupal (primary use was for a personal blogging platform, with a bit of extra extensibility and a well developed plugin ecosystem). Sadly, most of my knowledge has escaped me, so I’m starting completely from scratch knowledge wise, and I don’t know where to start.

Summary

I’m going to use Drupal as the platform to deliver an intranet for a small company I work for.

In order to make navigation as simple as possible, and without having to worry about themes and menus constantly – I’d like to have pages where it displays an automatically generated ‘table of contents’ for all the documents or items on one or more levels below it.

Explanation

I intend to structure and alias the content with a URL alias similar to directories in a file system, for example:

Marketing
 ⌊_ eCommerce
  ⌊_ Search Advertising
      ⌊_ Google
      ⌊_ Facebook
  ⌊_ Product Maintenance

Administration
  ⌊_ Vehicles
  ⌊_ Accounting and Finance

and so on

On the homepage, I would like to have a content block or something appropriate in the body, which displays only the L1 directories (i.e. Marketing, Administration), and that is then linked to their relevant pages (i.e. domain.com/marketing, domain.com/administration).

From there, the home pages for these L1 areas have an index that traverses and lists everything automatically at L2, L3 and so on

I hope what i’m trying to achieve has made sense, and appreciate all and any help to point me in the right direction for achieving this.