The downward-facing dog is a yoga pose with the goal to stretch the back, to fortify the dorsal muscles and, more in general, all the high part of the body.
In addition to this, this pose let you see things from another point of view.
Come onto your yoga mat on your hands and knees. The head is aligned with the backbone and the instep is lying on the floor.
Put your feet down and lift your knees away from the floor. The heels should remain away from the floor while the sitting bones go toward the ceiling. Your legs are slightly bent.
The goal of this exercise is to stretch the back, so try to continue to lift your sitting bones towards the ceiling but stop when you feel any kind of discomfort or pain.
Stay in this pose, the heels off the ground, legs slightly bent and sitting bones towards the ceiling, for some breathes.
Return to the initial pose on all fours