Thanks for the question!
When adding salt to roads and walkways, the salt acts to change the freezing temperature of the snow/water on the pavement. Isn't that neat! The freezing temperature lowers, and prevents the water from being able to freeze.
The actual reason that the application of salt causes ice to melt is that a solution of water and dissolved salt has a lower freezing point than pure water. When added to ice, salt first dissolves in the film of liquid water that is always present on the surface, thereby lowering its freezing point below the ices temperature.
