Antifreeze and engine coolant are the same product, sold in the same packaging, and both go into the vehicle's radiator. All gasoline engines need water to circulate through them to maintain a stable operating temperature. Antifreeze keeps the water stable across a broad range of temperatures, from freezing to boiling.
The active ingredient in most antifreeze brands is ethylene glycol, a kind of alcohol that bonds with water when the two are mixed in equal parts. The ethylene glycol lowers the water's freezing point from 32 degrees Fahrenheit to negative 30, and it raises the boiling point of the water to over 275 degrees Fahrenheit. This keeps the water in its liquid phase regardless of the outside temperature.