It contains iodine, although iodine itself isn't used in the preparation......
Iodised salt is simply standard food grade sodium chloride, that has very small amounts of ionic iodine compounds added to it.
The purpose is to prevent iodine deficiency in the diet; many people's diet doesn't include much or any naturally ocurring iodine. It is important to have small amounts of iodine in the diet for healthy functioning of the thyroid gland, amongst other things.
To prepare iodised salt, regular sodium chloride is sprayed with an aqueous solution of potassium iodide or potassium iodate.
The amount of potassium iodide or iodate required is extrtemely small, however. To make 1 tonne (1000 kg) of iodised salt, you only need about 63 g of potassium iodide.
But it should be noted that the element iodine is not used in the preparation of iodised salt, nor is it found in the finished product. It is iodine ions that are found in iodised salt, along with sodium chloride.