but I cannot find a documentation of the relations in kickstart.

Is ther something alike?

I'd need to know how things are wired together.

I found out, that product categories are used to generate the main menue (via taxonomy_menue).
I found the differerent content types, feeding different sections on the front page.

If there would be a documentation about these concepts, it would be much easyer to get a own shop running.

This way of trial an error leads to often to a one way into a blocked road.