How to remove discourse website

Thanks again.
But I wished if you could also answer my 2nd question, which I believe must almost be a single line answer.

I’ve googled to know this answer for around 1 hour.
And I’ve read this whole discussion on this topic on meta, here.

But I couldn’t understand.
I could repeat my dilemma:
Whether it is such that
There is Ubuntu OS, and then there is a normal docker installation in it/on it.
And in that docker installation there is Discourse docker running?
Or its simply Ubuntu Server OS and Discourse Docker installed/running in it?
Or it is not called ‘Discourse Docker’ but something else?

P.S: I also tried to understand the same thru this long topic post. But it just fell short of telling my query (almost did, but just not).