Yoga is not a exercise or routine of exercise only. Exercise are just a part of Yoga postures. Actually there are many differences between Yoga posture and exercise. Yoga postures need a different mindset, while exercise needs a sportive mindset.
Yoga is like a breeze and exercise is like a wind (rigorous exercises can be compared to storm). Every Yoga posture needs a slow and gentle transformation without any jerk or force, just like a breeze.
Starting Yoga is not like starting exercises where you have to warm up physically in order to do physical workout. In Yoga you have to warm up mentally in order to stay calm and natural while doing Yoga. Even before you reach these postures one has to learn and understand some basics, which lay the basic foundation.
Exploring Yoga is about these very basics which are either not discussed anywhere or are not understood clearly.