Advaya Taraka Upanishad belongs to the Sukla Yajur Veda and deals with the secret of attaining immortality by overcoming death and bondage. It speaks about the state of advaya, non-duality, and Taraka Yoga, the means by which you can attain union with the formless light inside and experience that state. Advaya (a+dvaya) means not two or a state of nonduality. Tara means anything bright and beautiful, a reference usually to a shining star.
In ancient times stars were used to navigate across the oceans and to travel in the dark. Taraka is that which helps you to travel across an ocean to cross over to the other side. Advaya Brahman is a state of non-duality or oneness with Brahman attained by overcoming ignorance and delusion. According to the Upanishad, one can attain this state by awakening the Kundalini. For that one has to see in meditation the inner light, the star, either in the top portion of the head or in heart, and use that light to navigate across the cycle of births and deaths to attain Brahman. By seeing the inner light in the head constantly and awakening the Kundalini energy one can enter the Turiya state. However, this yoga should be practiced strictly under the guidance of a qualified teacher. who must possess the following attributes: he must be a scholar in the Vedas, a devotee of Lord Vishnu, free from jealousy, an expert in yoga and its practice, and personify the ideals of Yoga. With his help one should enter the transcendental state of oneness in which the duality between and knower and the known is absent and nothing remains except the Self.