What are they for? i.e. what is the benefit of taking them?
They are just minerals in super fine particle form.
We are supposed to get minerals from vegetables, which draw them from the soil. Some argue that the main farming soils have been depleted of minerals for decades, and that they are no longer present in acceptable strength in our vegetables.
Minerals are essential to good health. As I understand it, you cannot properly absorb vitamins if you are mineral deficient.