Thawing salt requires water; because the thawing salt only lowers the freezing point of the water.
As is known, pure water freezes at approx. 0 °C, a saturated salt solution only at approx. -21 °C.
The more salt is dissolved in the water, the lower the freezing point of this brine.
So if you sprinkle salt on the ice, it must first dissolve in the water film. The de-icing salt thus lowers the freezing point of the water film and prevents it from freezing again.
This salt solution (brine) continues to thaw the ice until the freezing point of the brine has adapted to the temperature of the ice or it has completely watered down.
The salt solution (brine) is also used as a preventive measure! Mostly in the form of a 20 per cent brine solution.