It lows the freezing point therefore lowering the melting point

You can experiment with this concept at your house too

Get a large bowl, room tempeture can of soda, salt, and ice.

Add water and a lot of salt to the bowl. Stir up so the salt is dissolved into the water

Add the can of soda

Add the ice.

Now stir. You'll notice the ice melt fast. Faster the ice melts the faster the water will become cold.

Remove the can of coke and open it and taste. Should be ice cold.

Why? Ice cools water (or whatever) by absorbing the heat from the liquid or surface. In exchange the liquid or surface is cooled. The faster it melts the faster this exchange happens. It takes a lot of energy to cool things or to heat things. They will eventually meet equilibrium and be losing cold to the air or surface they are in contact with by conduction convection and well this wasn't supposed to be a complicated explanation so we'll just leave it at that.

Your house's ac works on this same concept sort of. It's not magically spitting cold air into your house it's sucking the heat out and passing it over something cooler then returning it back to your house. In the case of hvac it's compressed gas/fluid. Altitude and atmosphere effects the properties of things like the boiling point and ok im gonna stop