Should we believe in stones and stars?

I have a ring with a moh e najaf stone in it, can I wear it and what beleif should I have? and can it be worn in the left hand?

It is recommended to wear a ring in the right hand as it is the sign of the Shia. It is not haraam to wear it in the left hand.
The ring by itself does not have any power. It is only God who has power.