Well the simple answer to your question is that salt lowers the melting point of ice. But to be more specific, normal water freezes at 32 degrees Fahrenheit. When it’s mixed with salt, this temperate becomes lower and lower, so if say, you’re driving along a road and the temperature outside is in the 30’s, then sprinkling salt on the road would lower the freezing temperature and thus melt the ice. It would no longer be cold enough for the water to freeze. As for the process of the ice melting, the salt actually dissolves the ice as it mixes with it. However, salt can only be used down to a certain temperature. Any lower than 15 degrees Fahrenheit outside and salt won’t do you much good.