Tasmin sati svasaprasvasayor-gativicchedah pranayamah—“Regulation of breath or the control of Prana is the stoppage of inhalation and exhalation, which follows after securing that steadiness of posture or seat.”
This is the definition of Pranayama in the Yoga-sutras of Patanjali.
‘Svasa’ means inspiratory breath. ‘Prasvasa’ means expiratory breath. You can take up the practice of Pranayama after you have gained steadiness in your Asana (seat).