Question

why does using salt chill drinks so fast?

Answer 1

Why does using salt cause snow to melt much faster? (Analogy)

Answer 2

If you mean adding salt to ice, the salt lowers the freezing point of water, the ice melts, the heat to melt the ice must come from somewhere, and that somewhere is from the water in the mixture. That causes the water to become colder than zero degrees C.