Office 365 – How does the main menu of a modern SharePoint site become a dynamic sitemap?

I'm creating a modern SharePoint site as a documentation site for our end users. We want to create a basic hierarchy of folders and pages, and possibly pages with child pages.

📁Sales
    📄Creating a Lead
    📄Creating a Proposal
        📄Adjusting Prices
📁Administration
    📄Resetting Your Password

These are not just Word documents or other files in a directory, but modern SharePoint pages. My questions about building and maintaining this hierarchy are:

  1. How do I create nested pages, regardless of whether they are subordinate to a folder / section or another page? We do not want a flat list of pages.
  2. How do I display this hierarchy in the form of a sitemap in the main menu navigation? dynamic without having to manually create this hierarchy and edit it each time a new page is created?