"Quench" really means to use liquid on something until it has gone. So you quench your thirst by drinking; you quench a fire by pouring water on it. (You could smother a fire with something solid such as a blanket.)

Quenching can also be a technical term in metal working. It is used to alter a metal's properties, typically hardening.

To douse means to cover something with a lot of liquid. To smother- it kind of depends on the context but literally it means to cover a person's airways so as to stop them being able to breath. In the context of food, smoother could be used to describe for example a pizza 'smothered in cheese' i.e there is a lot of cheese on the pizza To quench is to drink liquid so that you stop being thirsty. hope this helps?