According to Hindu tradition the Ajna chakra is the 6th chakra center, which is located between your eyes and above the top of your nose. The Ajna center represents the third eye – the eye of intuition and intellect, its corresponding color is indigo, and its mantra/sound is “Aum”.
According to Wikipedia: “Ajna translates as “command”, and is considered the eye of intuition and intellect. When something is seen in the mind’s eye, or in a dream, it is being seen by Ajna. It is a bridge that links gurus with disciples, allowing mind communication to occur between two people. The sense organ and action organ associated with Ajna is the mind.
As Hindus believe that spiritual energy from the environment enters their body through this gateway, they take great care to protect it with spiritually positive protecting forces. The various religious marks on the foreheads of men and women belonging to the Hindu faith (like holy ash, namam, vermilion etc.) are the blessed spiritual prasadam of their respective forms of the Hindu gods.
Meditation upon Ajna supposedly grants siddhis, or occult powers, to quickly enter another body at will and to become omniscient. He realizes unity with Brahman; and he has the ability to create, preserve, and destroy the three worlds.”
It is believed the most effective ways to activate the Ajna center (in Kundalini practice) are through Trataka (steady gazing), Shambhavi Mudra (gazing at the space between the eyebrows), and some forms of Pranayama (breath exercises).
To learn more about the Ajna chakra visit: Chakra-Anatomy.com