Bluetooth ready car

[mazspeed]

Ok, I don't know how this thing works, but if someone can give me a clue on if this is a good thing to have or not. I have this new Alpine deck for the camaro, and My wife and I are getting new bluetooth ready phones, so how does this work in a car? I know the handfree thing, but how does this work in the car if you are playing the stereo or anything else. Do you talk into your phone, or car speakers or what. I'm sort of a tech idiot when it comes to this thing.