You need:
- a bowl
- a thermometer
- ice cubes
- salt
- some water
- something to stir with
Add water and ice cubes to the bowl and then add the thermometer. Stir a bit. What does the thermometer show?
Now add a little salt and stir well to solve the salt in the ice water. What happens to the temperature? What happens if you add even more salt? How cold can you get your water?
When a mixture of water and ice is in equilibrium, the temperature is at freezing point. When you add more salt, that lowers the freezing temperature (the more salt, the lower the freezing point) and the mixture is no longer in equilibrium.
Heat from the water is used to melt, and the temperature of the mixture sinks, either until all ice as melted, or until the temperature of the water is the freezing temperature.