‘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). If you can sit for 3 hour in one Asana, continuously at one stretch, you have gained mastery over the Asana. If you are able to sit from half to one hour even, you can take up the practice of Pranayama. You can hardly make any spiritual progress without the practice of Pranayama.
Apane juhvati pranam pranepanam tathapare; Pranapanagatee ruddhva pranayamaparayanah (Gita, Ch. IV-29.). Others offer Prana (outgoing breath) in Apana (incoming breath) and Apana in Prana, restraining the passage of Prana and Apana, absorbed in Pranayama. Pranayama is a precious Yajna (sacrifice). Some practise the kind of Pranayama called Puraka (filling in). Some practise the kind of Pranayama called Rechaka (emptying). Some are engaged in the practice of Pranayama called Kumbhaka, by impeding the outward passage of air, through the nostrils and the mouth, and by impeding the inward passage of the air, in the opposite direction.