Many people start yoga for the physical practice. A leaner physique, improved flexibility, a better sex life, all of which are relevant attributes to a regular Yoga practice.
With time, your practice may become deeper. Questions such as: who or what am I beyond my mind and body? How can I discover my ‘True Self.’
Atman (True self) refers to the concept of what is your underlying self? What is real and unchanging? Is it your body? Is it your mind?
It is neither of these things. Atman is a connection to your higher being, free from suffering.