Hi everyone, could you help me with the usages of join and join in? It’s really confusing to me.

Once you open an interesting book you suddenly see an interesting world having been mistakenly perceived. The world is so funny as the book you are reading, and you realize that there are numberless interesting books out there that you can’t finish reading just as they can’t finish writing. Would some strange idea occur to you at that moment that the authors of the interesting books are not living in a same world with you. But they are truly yes. So the world is comprised of two categories of persons: the one to write , and the other to read. Once the connection between the two is severed, we are found to be in a boring world, living a boring life, and waiting for a boring death. Nevertheless the world is created not to be boring or interesting rather to be perceptible.

How should I read and understand the word etymologicon?