There is a very good Ars Technica article on how an ISP works. It traces the whole network, from submarine cable through to last mile into a house. It was written in 2016, but I imagine it's still relevant:
Thank you, that was a great link for us uninitiated folks.
Also another great plug for ArsTechnica (even though the main article is them as well, and I'm sure most of this audience is well aware of them) and the excellent technical writing they do.
https://arstechnica.com/information-technology/2016/05/how-t...