1. It is universally known fact that lord Shiva has three eyes. It is said that the sun resides in the right eye, the moon resides in the left eye. 

2. The eyes are there for outward perception, to see the world as it is. The third eyes the eye of knowledge. It is to see that which is beyond perception. 

3. In the beginning of times, when Brahma and Vishnu both were looking for the source of energy-that came there as a beam of light. They could not find it, and Brahma decided to lie about it-just to prove his superiority. Shiva came out of the beam, and the whole energy coiled up at his forehead into his third eye. This itself proved the power of Shiva. 

Shiva used his third eye to create as well as destroy. 

 - After the death of his beloved wife Sati, Shiva went into a deep reflective state ‘Samadhi’, and refused all worldly attributes. Nevertheless, for the survival of the world it was necessary for, Shiva marries and parwati to be the goddess the world needed. To wake him up from the samadhi kamdev shot an arrow which would awaken the desires in shiva and he would come out do his pensive state. 

-  As soon as the arrow struck Shiva’s heart, all three eyes opened at once. The energy from his third eye was so strong that kamdev could not bear it. His body turned into ashes. Some say that Shiva that it was Shiva's way of negating the desire. This cannot hold true, as Shiva is said to equal to thousand kamdev. He is the one who gave us kamshastra. He is  the creator of carnal attributes. He does not negate desires. He is in-fact the origin of all desires. It was not his denial of desires, rather it was his sudden awakening that burnt kamdev. 

- Once parvati shut both his eyes in an act of playfulness not realizing that by shutting his eyes the world turned dark. The universe lost all his light as the sources of light the sun and the moon were both in shiva’s eyes. Shiva, thus had to open his third eye to restore the brightness of the world. The heat of his third eye way so robust that parvati’s hands perspired, and the drop of sweat flowed down to the earth. From this drop of sweat, Andhak, a sightless asura, who was as tough as shiva himself was born. Andhak was unsighted because he was born as a result of the blind state of his father Shiva. 

- The Adiyogi Shiva, who is the introducer of yog sadhna, or yoga as it is commonly called, is envisioned having a third eye in his fore head also known as the Ajna chakra. This is the sixth energy point in our body, which is associated with higher consciousnesses. Yes! Every human has it. Then why is it shiva who is pictured having a third eye. As I mentioned earlier, Shiva is the creator of yog sadhna. His third eye is all powerful. This is the delineation that if one follows the yogic lifestyle, he is capable of opening his third eye. When your third eye is activated, you can see beyond perceptions. Your physical eyes can only see what can be comprehended, but your third eye can see that which is not comprehensible.