Synthesized answer
The provided passages do not contain enough information to explain the key concepts of "Understanding Media: The Extensions of Man" in my own words. The passages only consist of the title of the book and its author and publication year [1]. They do not offer any explanation of the book's core ideas.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: Rare Marshall McLuhan / Understanding Media The Extensions of Man 1964 - NY by Marshall McLuhan