Libertarianism and anarchism, a brief precis

[disclaimer: these paragraphs are coming from a ground-level normie understanding and I have not read up on things to a level that a properly educated libertarian or anarchist would not find risible. My understanding is one achieved by an interested amateur whose primary dialectic skill is sounding a lot more versed and confident in a given topic than is actually the case.]

A pal elsewhere asked for clarification on the difference between libertarianism and anarchism, specifically vis-a-vis taxation and force, and my answer ran a little long.
( tldr: a distinction without much of a difference, but with caveats )