An introduction to Debian's topology/structure/???

[Richard Owlett <rowlett@cloud85.net>]

"Topology" may be a poor word choice.

First I'm looking comparison of required, important, standard, optional, 
and extra as package labels [particularly interested in corner cases]. 
I've been looking at [https://www.debian.org/doc/debian-policy/]. I'm 
not grasping something. Not sure what ;/

Similarly for Depends, Recommends, Suggests, etc. I'm currently reading
[https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_package_dependencies]
Other suggestions?

TIA