The practice of Hatha Yoga comprises of those sadhanas which are primarily concerned with the gross body, sthula sharira.
The popular meaning of the word Hatha is a force, a violent action, a will power.
The functioning of the body means the functioning of all the three that is, the body, mind and senses.
Vasana is the past impression and samskara is a subtle impression.
Hatha Yoga is a disciplined practice. If one practices Hatha Yoga following the steps one succeeds in his goal easily.