You cannot do yoga. Yoga is your natural state.
“You cannot do yoga. Yoga is your natural state. What you can do are yoga exercises, which may reveal to you where you are resisting your natural state.” ~ Sharon Gannon
Asanas are known as the physical practice of yoga. Yoga itself is almost entirely a mental practice, the physical practice being a tool used to get deeper.
That being said, a physical practice of yoga is very powerful for the body and mind, as well!