I watched a beginner tutorial on it because I wanted to know what it was too. It's not a lot different from the component system that's already in VRCHAT, but it looks like it has more functions and is, of course, more visual. I've been working building worlds for a month or two and I understood pretty quickly how to use PlayMaker. I don't have it yet, but I am looking forward to getting it. ($65...)
The devs have said some C# scripting will be possible, but I can see how there's massive room for abuse there, so don't know how they're going to prevent it. PlayMaker seems like a nice medium.