What is Yoga ?
The word yoga is derived from Sanskrit origin, you meaning to bind, join ,attach and yoke, to direct and concentrate one's attention on ,to use and apply .It thus means union or communion .Ti is the true union of our will with the will of god .It thus means says Mahadev Desai in his introduction to the Bhagwat Gita according to Gandhi the yoking of the power of the body ,mind, and soul to god ;it means the disciplining of the intellect, the mind, the will, which that yoga presupposes; it means a poise of the soul which enables one to look at life in all its aspects evenly.

Yoga is one of the six orthodox systems of Indian philosophy .It was collated ,coordated and systematized by Patanjali in his classical work the yoga sutra ,which consists of 185 terse aphorisms .In Indian though , everything is permeated by the supreme universal spirit (Paramatma or go)of which the individual human spirit (jivatma)is a part .the system of yoga is so called because it teaches the means by which the jivatma can be united to ,or be in communion with the paramatma;and so secure liberation (moksa).

The one who follows the path of yoga is a Yogi (for men) or yogini (for women)
In the sixth chapter of the Bhagavad Gita ,which is the most important authority on yoga philosophy, Lord Sri Krishna explains to Arjuna the meaning of yoga as a deliverance from contact with pain and sorrow .It is said When his mind ,intellect and self (ahamkara)are under control, free from restless desire , so that they rest in the spirit within , a man becomes a yakta -one in communication with god . A lamp does not flicker in a place where no winds blow ; so it is with a yogi , who controls his mind , intellect and self , being absorbed in the spirit within him .When the restlessness of the mind , intellect and self is stilled through the practice of yoga , the yogi by the grace of the spirit within himself finds fulfillment .Then he knows the joy eternal which is beyond the pale of the senses which his reason cannot grasp .He abides in this reality and moves not there from .He has found the treasure above all others .This is nothing higher then this .He who has found the real meaning of yoga -a deliverance from contract with pain and sarrow"?

All sessions .of yoga begin with the Surya Namaskar ,or sun salutation This excellent
warming-up exercise consists of a sequence of 12 position that moves the spine in various
ways and promotes flexibility .To stiff people and to the elderly ,it helps the body to gain
flexibility. It also regulates the breath and focuses the mind.

There are many types of physical exercise ,but the yogic system of asanas (a sanskrit word menaing "steady pose") is the most ,benefiting far more than just the physical body .

The Asanas emphasize deep breathing ,relaxed movements ,and mental concentration.

Asanas are designed to promote a state of mental and physical well-being, or good health.

This may be defined as the condition that is experienced when all the organs function efficiently under the intelligent control of the mind.Asanas have an extraordinary capacity to overhaul ,rejuvenate ,and bring the entire system into a state of balance . Although they are performed by the physical body, Asanas also have profound effects on the Astral Body.

As purity of body encourages purity of mind, Yogis have developed the six cleansing techniques or "shad kriyas", for purification of the physical body. Through this simple exercise, Nature is assisted in the elimination of waste products and many mental and physical complaints are eliminated.

In yogic breathing exercise, or pranayama, the best is seen as the important link between our physical and mental aspects.Pranayama cleanses and strengthens the physical body, but it's most important benefit is for the mind which it claims, steadies and clears.

Meditation is a natural state of consciousness that is not "learned", any more then you learn to sleep. When the mind becomes concentrated and steady, it will naturally go beyond the normal mundane awareness into the state referred as meditation.