Svadhyaya, or self-study, is the fourth niyama. As with the other niyamas, this is a process of discovery that we can pursue our entire life.
There are generally two ways svadhyaya is considered. First is the study of sacred texts. In the yoga tradition, yoga texts like the Bhagavad Gita, the Vedas and the Sutras are considered. But there are sources of wisdom and guidance in all the world's traditions. All have value and can be sources of inspiration, clarity and understanding.
Second is the study of our own self. Reflection and meditation on who we are, how we are in this world, what our motivations, strengths, limitations, fears are. Every day is an opportunity for this reflection! Every moment we have a particular outlook on what is happening and how we are responding. This is not always an easy task. We will not always like what we see. Remembering the yamas, tho, we must look with truthfulness and accept ourselves with non-violence. With an eye of compassion and heart of love, we can see that we have choices in our response. As we meditate and study, our world view and our understanding of ourselves will shift and grow.
We stick with the study (tapas!) and the potential for healing and growth is enormous. We will find ourselves comfortable in our own skin, loving and kind to those we meet, living in cooperation with others, appreciating the great diversity of divinity we have in our world.