How do you make money off Youtube?

I’m planning to, but I get confused by making an AdSense Account with Google. You have to do that, right? The thing is I don’t want to enter anything yet unless I absolutely understand what this means. Because I read somewhere in the AdSense terms that you need to fill out a W-40 tax form or whatever? Does this mean that I would technically be under employment by Google/Youtube? Like. . .is this legally a “job” then? Because if so, I’m not sure if I’ll go through with it. If you’ve done this, I would appreciate all the details of how this works. (But even if you don’t but know all about it, obviously pray tell)