Two fingers above the rectum and two fingers below the linga , four fingers in width is a space like a bulbous root.
Between this space is the yoni having its face towards the back.That space is called the root;there dwells the Goddess Kundalini.
It surrounds all the nadis and has three coils and a half;and catching its tail in its own mouth,it rests in the hole of the Sushumna(nadi).
Significance-
Chandogya Upanishad 8.6.6 and Katha Upanishad 2.16 says:
यदा सर्वे प्रभिद्यन्ते हृदयस्येह ग्रन्थयः ।
अथ मर्त्योऽमृतो भवत्येतावद्ध्यनुशासनम् ॥
शतं चैका च हृदयस्य नाड्य-
स्तासां मूर्धानमभिनिःसृतैका ।
तयोर्ध्वमायन्नमृतत्वमेति
विष्वङ्ङन्या उत्क्रमणे भवन्ति ॥
When all the knots of Hridaya Granthi are cut down, mortal becomes an immortal & attains Brahman there. There are 101 Nadis which emerge from heart, one Nadi goes out piercing the head. Going up through that, one attains immortality; the others serve for departing in diiff. ways.
According to swami vivekananda-
“There are two nerve currents in the spinal column, called Pingalâ and Idâ, and a hollow canal called Sushumnâ running through the spinal cord. At the lower end of the hollow canal is what the Yogis call the "Lotus of the Kundalini".
Yogis describe it as triangular in form in which, in the symbolical language of the Yogis, there is a power called the Kundalini, coiled up. When that Kundalini awakes, it tries to force a passage through this hollow canal, and as it rises step by step,
as it were, layer after layer of the mind becomes open and all the different visions and wonderful powers come to the Yogi.
Kundalini energy can be activated by various means like yoga, breathing techniques (pranayama), certain herbal preparations,
creating particular vibrations in the body through the chanting of mantras, and through initiation (energy transmission) by a yoga adept whose Kundalini is already awakened. Of these, initiation is the fastest, easiest and safest way of awakening Kundalini.
But the process to activate this sleeping Shakti can not be learned by reading books. It can only be learned from a Siddha Guru(one who has mastered the process himself) as rightly said in one of the comments under your question.
However, the first symptoms of an activated Kundalini are :
The brilliancy of the body is increased,the gastric fire becomes powerful,and freedom from disease,cleverness,and omniscience ensue.
(Siva Samhita, chapter 5:65)
The scientific research-
An attempt to record Kundalini activation and its physiological effects was made by Itzak Bentov (1923- 1973), a Czech born scientist, inventor, mystic and author, and a pioneer in the field now recognized as ‘consciousness studies.’
Bentov developed a model that attempted to explain the effects of Kundalini Awakening on brain activation. According to this model, when Kundalini ascends the spine through the sushumna nadi (the main channel of subtle energy), it results in a huge energy influx into the brain.
As the Kundalini flows from the thalamus to the cortex, it sets up a powerful energy loop within the brain, generating coherent alpha and gamma waves, and awakening the dormant, non-mechanical parts of the brain which we have never used before.
With increasing levels of coherence, the whole brain comes alive, turning into a super-conductor of conscious energies that heal, empower and transform our lives. Enhanced awareness levels, greater creativity and extraordinary abilities start to express through us like
levitation, teleportation and materialization. Brain activation is also known to slow down the ageing process and improve immunity to disease.
