I love doing yoga, it is so relaxing and calming!  I especially like Hatha yoga and Rāja yoga
That's great! What exact are Hatha and Raja yoga? What are the differences?
Rāja yoga is sometimes called "royal yoga" or "classical yoga" while Hatha yoga is mainly supplementary physical techniques within the broader concept of Yoga.
I'm not very familiar with yoga. What is the basic concept or classical approach?
I'm not sure, but generally yoga is a group of physical, mental, and spiritual practices
When did it become so popular? I know so many people who enjoy it.
It became popular in the 1980s in the Western world.
Where did it originate?
There has been speculation that yoga dates back to pre-Vedic Indian traditions
Do most people do it for physical reasons or for religious reasons?