There are four steps in Raaj Yog practice -- Pratyaahaar, Dhaaranaa, Dhyaan, and Samaadhi.

(1) Pratyaahaar occurs when Kundalinee Shakti leaves Moolaadhaar Chakra (Point between Urinal and Anal outlets) to Swadhishthaan Chakra (the base of the spinal cord).
(2) Dhaaranaa occurs when Kundalinee Shakti reaches Manipoorak Chakra (Navel point).
(3) Dhyaan occurs when Kundalinee Shakti reaches Anahat Chakra (Solar Plexus).
(4) Samaadhi are of two types - comprising of Sa-Vikalp Samaadhi (Vikalp means difference - Jeevaatmaa and Paramaatmaa are different from each other), and Nir-Vikalp Samaadhi (Nir-Vikalp means no difference ie Jeevaatmaa and Paramaatmaa are one and only one).
--Sa-Vikalp Samaadhi occurs when Kundalinee Shakti reaches Vishukti Chakra (Throat),
--Nir-Vikalp Samaadhi occurs only when Kundalinee Shakti pierces and passes though Aagneya Chakra (between the eye brows), and proceeds to Sahasraar Chakra (between right and left brain lobes) This is identified as Pineal Gland which will shed Sudhaasaar water when pierced by Kundalinee Shakti.

Hence Kundalinee is the Shakti and Sahasraar is Shiv, and Shakti during every birth tries though the 6 Chakra to reach Shiv and when she reaches and mingles with Shiv, the birth and death sequence of that particular person ends, and the person will reach Moksh (Merging with the Supreme Almighty - Para Brahm).

Our Physical body (Sthool Deh or Sthool Lok) is in 3rd Dimension. Inside it is the Astral body (Sookshm Deh or Sookshm Lok) which is in 2nd Dimension. Inside it is our Causal body (Kaaran Deh or Kaaran Lok) which is in 1st Dimension. Inside it lies the Aatmaa in Brahm which is in Dimensionless State.

Though the Aatmaa or Brahm is the same in every body, the other bodies viz. Kaaran Deh, Sookshm Deh and Sthool Deh differ due to Kaarmic outcomes or fruits of the Aatmaa's deeds in earlier births, and hence the palpable difference, but the Aatmaa or Brahm is one and only one.