What we have here is sodium chloride with some stuff added to prevent caking. The salt comes out of the giant salt domes that were formed long ago when seas evaporated. The salt is dissolved in water and then all impurities are removed. But don't let the anti-salt police get to you. The human body needs salt to function properly, especially in hot weather when salt is lost from the body through perspiration.
Iodized salt is regular table salt with potassium iodide added.
The potassium iodide is to prevent goiter in those folks who don't get enough sea food products in their systems. Sea salt is very popular with the natural food folks. Sea salt is made by evaporating sea water. Sea salt contains many trace elements and other things that are good for you. It will be coarser grained than regular table salt, and many say it has a better flavor.