Easy question first - yes, everyone can see this. You should see a little box that says 'private message' on it and if you pick that, messages can only be seen by you and the recipient/s.
As for how they get there... Well, I don't know much about making web pages, honestly. It's like... Hm. Putting together a clock? The coding languages are gears and springs. Individually, they're useless. Together, they make the internet.
People like cats. They're cute and dumb. And anymore, they're much cleaner.