How do you draw an explanation of how water is made in a car engine?

If you are referring to the water that drips from the exhaust when the engine is running, it is formed by the burning (oxidation) of the carbon and hydrogen that makes up the gasoline. When the carbon/hydrogen molecule combines with oxygen during the burning process, carbon dioxide and water are formed. The water vapor condenses into liquid form as it passes through the exhaust and we see it dripping out as water.