Yoga is a very complex and broad concept and is impossible to describe in a few lines. In its essence, the true yoga is about breath, it’s a breathing technique. Breath taken in the right measures and released from the body in the right measures will alter your thought process virtually immediately.
Yoga is the sound vibratory frequency.  The sound constantly vibrates in our body. The physical aspect of yoga comes in because certain exercises and postures makes that sound vibrate (better) in your body.