Asana is typically translated as the physical postures, the parts we associate as yoga. It must be graceful, stable and done with ease.
Prana literally means the life force, the energy, which flows through all. Ayama means expansion. Pranayama is the prolonging of our life force and energy. Pranayama teaches us to be calm, collected and centered. As the breath becomes still, slow and steady, we find that in our lives also we bcome still and steady.