Netsh is a tool. How do you first learn about any tool? You typically learn from somebody that knows how the tool works and, more importantly, knows what the tool is useful for.
Over the last ten years, search engines like Google and Q&A forums like Superuser have facilitated encounters between people who need the knowledge and people who have the knowledge. You've already commented on this.
Back in the stone age (which always ended about ten years ago), there was face-to-face Q&A, presentations and lectures, and tutorial documentation. There are probably some excellent tutorials out there that introduce the Windows user to networks, and many of them probably bring netsh into the discussion. These vehicles reached a comparatively limited audience.
Here's the good news: over the course of your life time, you can expect to add considerably to the array of tools and techniques you can draw on in any given situation that calls for diagnosis and repair.
Here's the bad news: Over time, you can expect much of your knowledge base to become obsolete.
Here's more bad news: while you are expanding your knowledge base, the total knowledge base is expanding at a much, much faster clip.
So, over time, you can expect to become absolutely more knowledgeable, but relatively more ignorant.
Welcome to the club!