Patanjali is called many time father of hatha yoga, which is a misconcept, yoga is 5000 years old. The truth is Patanjali has managed to bring essence of yoga in his book yoga sutra of Patanjali with 196 sutras, explaining the deep meaning of different kinds of human suffering, detail and scientific way to be free of suffering and reach to internal happiness.
Patanjali has divided those sutras in four parts
1. Samadhi Pada (51 sutras)
In this chapter he explains in details the meaning of yoga, including different kind of vrittis (mind patterns), giving definition of different kind of samadhi, further he explains the obstacles in path of yoga and how to remove them with single pointedness. With help of meditation in the practice, different kind of samadhi one can experience till one reaches to the pure consciousness.
2. Sadhana Pada (55 sutras)
After giving brief understanding of yoga and the fruit of its practice he goes into detail explanation of suffering and cause of it, and how with discipline we can come to self realization. Ignorance, Ego, attachments, greed which are cause of suffering and how can it be reduced by discipline of yoga. He gives eight steps to the Samadhi (enlightenment). He explains the first five steps in this chapter : Yamas (Virtues), Niyamas (Discipline) , Asana( Physical posture), Pranayama(Breathing techniques), Pratyahara (Mastery over the senses).
3.Vibhooti Pada (56 sutras)
Here He talks about the rest three steps : Dharna(Concentration ), Dhyana(Meditation) and Samadhi(Pure consciousness), and how they are interconnected with each other, than going in details, brining awareness to power of practice and how at different stages Ego could be obstacle in samadhi. Bringing one’s attention to the result of this practice. how the awareness of body, mind can bring one to realization of self.
4.Kaivalya Pada (34 sutras)
The last chapter explains the ultimate union of self into selflessness, merging of energy and matter. Explaining the perceptions of mind and self illumination. with an awareness to look at the self and cession of distinction and realization of our natural form of Pure Consciousness.He has gone in details with small explanation of it.
If you like to read a deeper meaning and explanation of patanjali yoga sutra the best book is by Swami Satyananda Sarswati, “Four chapter of freedom”. Also there is a small pocket book with commentary by Swami Vivekananda, who took yoga to America in 1893 in first world’s religious Parliament.