The burning of fuel by internal combustion engines results in power, but it also results in noise, heat, and exhaust gases. Your car's muffler is responsible for helping to suppress the noise that's produced. Heat produced is absorbed somewhat by the radiator fluid and motor oil, but most of it's carried away in the exhaust. The exhaust also contains some potentially harmful substances. The catalytic converter helps to transform these gases to harmless materials by using heat and a chemical reaction. A product of this reaction may be a small amount of water. So a little steam or water coming out of the tailpipe is normal. Your car's exhaust system should be checked periodically to make sure it's functioning properly. Powerful smells or excessive noise could mean that your car has a damaged exhaust system. Contact a qualified mechanic in your area for more information on your car's exhaust system.