It's believed that there are three types of evil eyes
The first are unconscious evil eyes. These harm people and things, without intending to. The second type intends to harm. The third one is unseen, hidden evil which is the most evil one.
The Nazar Charm (Evil eye) is an "eye", often set on a blue or black background. It stares back at the world to ward off the evil eye and keep you safe from harm.
The bead reflects the evil intent back to the onlooker.