Turn on your a/c and let the car run for a while. You should have a puddle of water under the car near the right side of the firewall. For the rear sunroof drains, open the sunroof and pour water in the back, sides of the sunroof channel and the water will drain out behind the rear wheel wells.
Same principle. The firewall protects the driver/passenger cabin from unwanted intrusions from the engine bay. Its the partition that separates the two. It's right behind the battery in the plenum of the engine bay. Look for the water under the middle of the car just in back of the front passenger side tire.