When you want to use salt in your vaporizer you put the salt into the water reservoir where you put the water.
Add the water to the reservoir of the vaporizer and then add around 4 to 5 tablespoons of salt to the vaporizer reservoir water.
Then turn the vaporizer on like normal and the water will be dispersed into the air as steam.
When you add salt to a vaporizer it disrupts the bonds between the water molecules and slightly raises the temperature at which the water boils.
So some people add the salt to the vaporizer to get the vaporizer steaming faster in certain areas where it may take longer for the water to start steaming in the vaporizer.
I've never had to add any salt to the water in the vaporizer but some people do need too.