The origins of yoga have not yet been identified but the Patanjali Yoga Sutras remains one of the most influential works of Yoga practices and philosophy today. Yoga, one of the orthodox systems within Hindu philosophy, a psycho-physical practice of attaining unification with absolute reality (Brahman). When Yoga started developing there were endless amounts of schools teaching yoga with an emphasis on different aspects of yoga. There was no streamlined structure so it began to become impractical. Patanjali realized this and decided to codify Yoga into 196 sutras. Patanjali, who was one of the 18 classical Tamil Siddhars (sages and intellects) was not only a great grammarian but also wrote texts on medicine and Yoga Sutras. Although he did not originate yoga, he distilled the essence of yoga into the Yoga Sutras and became known as the ‘father of modern yoga’.
Yoga comes from the Sanskrit word, yuj ‘to unite’ and implies a union of the mind, body, spirit, and the divine. Sutras are principal texts, therefore the yoga sutras act as guiding principles to liberation (moksa) through the oneness of a spiritual path to self-realization. The Yoga Sutras are divided into 4 chapters, first chapter Samadhipada (a chapter on concentration), the second Sahanapada (chapter on practices), the third Vibhutipada (chapter on supernatural powers), and the fourth pada is called the Kaivalyapada (a chapter on liberation).
The first chapter, Samadhipada, starts with the sentence “... and now, Yoga.” What Patanjali means by starting the chapter in such a way is that once you feel your desires and goals fulfilled and you are looking for another, more spiritual form of fulfillment then it's time for Yoga. The second chapter, most important for a Yoga practitioner, Sahanapada, describe the practices to follow the path of Yoga. Kriya Yoga, a self-study, discipline, and orientation towards the idea of pure awareness are also mentioned in this chapter. Patanjali speaks of the obstacles towards the path of yoga such as the ego and attachment which can be overcome by Yoga. He believed the wise see suffering in all experience, the good and the bad. The fourth chapter, Vibhutipada contains 55 Sutras and starts with the Eight-Faceted Path (Asthanga Yoga) through which one may acquire siddhi (supernatural powers). The Vibhutipada also explored the concepts of meditation (dhyana), concentration (dharana) and Samadhi (contemplative union). The third chapter can only be accessed and executed once you have completed and experienced everything in the first two chapters.
These sutras are more philosophical in nature than practical, although they do specify what does what in the system it is not be read logically. Depending on your intention of how you want to approach the system you yourself can create your own Kriya. Eventually, the mind and the body become one, conquering the techniques in the Sutra, and then liberation can be achieved.