Of course there are flaws in the analogy, but it's pretty simple as long as you don't go ridiculously deep. But you get the point as a superficial analogy. You look out through the eyes(windshield) and mentally drive your body around. If you leave the car on, it can run by itself (regulating heart beat and breathing) but it can't do anything beyond that. Eventually without someone putting in the gas, the car would stop running (food and hydration). If you want to get really specific and stretch it, meditation could be considered leaving the car via the 'car door'.