Pranayam : The Prana is the base energy of this Universe. It is this Prana energy that resides in our body in five different forms which is identified as Pran, Apan, Vyan, Udan and Saman. These energies are situated in the different organs and parts of the body and until we are not able to keep them balanced at their optimum levels in their respective places till then we cannot attain physical and mental health nor can we achieve perfection in our works. Pranayam is  science emanating from Yoga, the regular practise of which can help us achieve optimum mental and health goals as well as allows us to work in perfection with our strengths in balance and achieve our inherent spiritual goals.

Come, let us understand this science of Pranayam in a simplified manner:
The action of carrying out the acts of Purak, Rechak and Kumbak forms the constituents of doing Pranayam. The act of inhaling our breath and filing up our lungs with air is known as  Purak, while the act of exhaling our breath with deep breathing out is known as Rechak and when we try to control our breath and hold it , the same is known as Kumbak. However it is only when we are able to control these three acts through optimum techniques and practice, than the collective act in the correct cycle of Purak, Rechak and Kumbak is known as Pranayam.

The act of Pranayam and Ayam is a well research scientific technique which should not be practised without the blessing of a knowledgeable Guru who would guide us through this ancient and scientific practise as without such expert guidance it would only be reduced to mechanical inhalation, holding of breath and exhalation without providing the doer of such Pranayam its true benefits. Ayam means the time period between consecutive breaths and its control and details.

Pranayam is the fulcrum of Yoga, with the science of Pranayam being the pivotal centre of a human being’s life , with each new breath giving us a sense of new life and every exhalation representing the destruction of the destructive elements in our body, and although the act of inhaling and exhaling is carried out by each and every individual, it is only under the guidance and nurturing of an able Guru that the above act translates into Pranayam. You would be wondering why there is so much emphasis on an “able” Guru for learning the act of Pranayam. This is because it is only under an able Guru’s guidance that the details and intricacies of Pranayam are revealed and without an able Guru’s blessing and teachings the same would not be possible. Further it is imperative to realise that Prana (Breath and its technique) have a direct correlation to our mind, brain and ego. Any Yoga practitioner shall be able to accomplish the task of teaching you the art of breathing and mechanical actions in the Pranayam, but it is only an able Guru under whose guidance and teaching can one be able to control the process of Pranayam and achieve stability in our mind and brain. It is due to this direct correlation that it said like mind like breath or like breath, like mind. Thus both are inter connected and entwined together and complement each other.
The state of attaining optimum Kumbak is a direct resultant of Purak and Rechak, which is effect takes us toward eternal joy. Summarizing and elaborating on this science , Shree Krishna in 4th chapter in the Bhagwad Gita has stated

अपाने जुह्वति प्राणं प्राणेऽपानं तथापरे ।प्राणापानगती रुद्ध्वा प्राणायामपरायणाः ॥

The above simpliciter means that under the guidance of a blessed guru we are able to interchange the Prana Vayu to Apana Vayu and vice versa and as a result we are able to attain simple Kumbak and transit into a Pranayam state.
When the breath is in a controlled and organized fashion kept in a Purak and Rechak rhythm, we are then able to attain a joyous Kumbak state. This state is able to calm all the Naadi Tantras in our body as a result of which all are worldly cravings and external tendencies are destroyed and accordingly advances our deep spiritual belonging.

On the other hand if we do not carry out the act of Pranayam in the correct fashion, than it can result in several types of diseases and physical ailments in our body. To conclude I would like to state that Pranayam requires continues practise and we can end all our external oriented worldly cravings by this regular practise and enlighten a divine light within us which is reflected in our countenance. 

Therefore Lord Adi Shankracharya has said that getting rid of all mind delusions is the attainment of Rechak and the feeling of I am the soul is the attainment of Purak and these above experiences being embedded in our conscience is Kumbak and this is in its entirety is pure Pranayam.