Media_dir configuration

I have a HA in Docker (Debian).
This is what I see:

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Since I have no floppy / cd-rom / usb stick, I cannot find out what are these enigmatic “folders” for.
What is a meaning of these “folders”?

Also, I see a button on the right top corner:

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“manage” what?

After pressing the button I see this:

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And each label is absolutely confusing:

  1. Where these media files not found?
  2. What means “folders cannot be managed”, how are they supposed to be managed - via yaml?

If I press the “Add media” button - I see a Windows Explorer. After selecting a small mp3 file this is displayed:
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I got an impression that this whole functionality is like an alpha version of some functionality which:

  1. has no clear Docs
  2. was not tested
  3. not user-friendly.

May be it works. But where it is documented then?