Dumb it down for me if you can.

[Aoi Magi]

There is also a reason one can crop an image and make it your tiny avatar. Back in the 70s an ABBA ALBUM jacket would be as big as a 1800s film square. I am trying to understand how you go from light being absorbed or refracted from an original source, being early photography, to copying that same film to larger pieces of paper through chemical process.

It's the same way the light got on to the tiny film, just played in reverse.

Essentially you put the "developed film" (where it is stopped from absorbing or being effected by light through chemical treatment) in a enlarger and shine light through it on to a larger photo-sensitive piece of paper and then put this paper in a chemical bath to lock it's photo-reactive state.