a) For an ELI5, this is like asking for a full course in the "basics" of networking. Too much

b) It is technical. There is no way around it. It is like asking for a lesson in quantum mechanics without referencing physics. Not really meaningfully possible.

c) There are logical functions (translation of symbols/information) and physical hardware and then actual products (which incorporate a variety of functions and physical hardware). Think of it as a home address (logical/symbolic) vs the home (physical) and the postal service (a combination of using logical function and physical to provide a service). Without a clear appreciation of the differences (again technical), it would be hard to explain all the things you asked.

A starting point might be the OSI model to understand the conceptual framework of networking and communications. Then the various functionalities etc will make sense.