“The word yoga means to ‘unite’ or ‘oneness’ and is derived from the Sanskrit word yuj, which means ‘to join’. This unity or joining is described in spiritual terms as the union of the individual consciousness with the universal consciousness. On a more practical level, yoga is a means of balancing and harmonizing the body, mind and emotions.” This is done through the practice of postures (asana), breathing (pranayama) and relaxation (shavasana & Yoga Nidra). More advanced practices include bandhas and meditation.
“Physical and mental cleansing and strengthening is one of yoga’s most important achievements. What makes it so powerful and effective is the fact that it works on the holistic principles of harmony and unification. According to medical scientists, yoga is successful because of the balance created in the nervous and endocrine system which directly influences all other systems and organs of the body.”
Yoga is experiential knowledge and this is different to intellectual knowledge which is gained through books and study. So the best place to start is on the yoga mat!
Reference text: Asana, Pranayama Mudra Bandha. Swami Satyananda Sarawasti, Yoga Publications Trust, Munger, Bihar, India.