To me, consciousness is the collection of electrochemical signals traveling throughout the brain. I'm plural[0], so I also believe in brains that have more than one consciousness, as I've personally experienced a similar thing before. But really, I don't know which signals make up consciousness, or where they are. I don't know how metacognition forms, either. And I don't know a real, physical explanation of plurality. I know just enough to play with the concepts, and in my opinion, that's enough. You can still say things about consciousness without knowing all the details, because most people will be able to form some idea of what it means based on how you are using it. So I think saying we don't know how to start it is still reasonable, even if we don't know what it is we're even trying to start in the first place.