Very simple, all water cooled engines,circulates water through their radiators,incoming ram air cools water down, thus cooling your engine down.
Never, and I MEAN NEVER attempt to remove radiator cap when engine is hot...NEVER DO I MAKE MYSELF CLEAR.
Because the water in system is heated to over 160 degrees, and is under pressure, if you remove the cap you can get seriously burned yourself or be blinded with antifreeze chemicals.
If you have to remove radiator cap "ALWAYS DO SO WHEN ENGINE IS COLD"!!!
Most cars today have a overflow plastic container attached to fire wall or inside fender, they have level indicator marked coolant level, when coolant level falls below this mark add more coolant.
You can learn more about cars on my blog
www.nrmcashin.com