PLEASE HELP!!!!! What is the moonstone and wat does it do??????

The moonstone is a stone (obviously) that Trevor gave Katherine to montrer Rose that she is to be trusted, he was of course proved wrong to trust her and ended up dead 500 years later. As Rose recently explained the moonstone binds the sun and the moon curse and elena is what breaks it (along with a witch-bonnie(for the spell), vampire-caroline, and werewolf-tyler).