yoga is a very good exercise to engage in, do you do it?
I do not but I hear it is useful for relaxation along with meditation.
so what is its usefulness?
Really it depends upon the person, but in Indian culture it is meditative and spiritual
really, so who invented it?
That's difficult to say. The origins are said to have likely come about in the fifth and sixth centures (BCE)
wow, so which country is yoga more popular?
Again, it's hard to say but I would assume it's still India although its origins have scattered across the world