In yoga, it is commonly said that the breath links the body and the mind.
Our bodies are always in the present moment and in the present space. Our minds, on the other hand, spend most of the time somewhere other than the present moment and space. We spend so much time thinking about the past and the future, which automatically takes us out of this moment where our body is located.
The technique of training the mind to focus on the breath brings our mind back into the present moment to join our bodies as we place our attention on the feeling of the breath moving in and out of bodies.
Try it for a moment. Notice the feel of the cool air as it enters your nostrils. Notice the feel of the warm air on your nostrils as you exhale. Notice how your body expands to make room for each inhale and how it softens on each exhale. As your mind wanders, continue to gently bring your focus back to your breath and just be aware of each breath entering, filling, and leaving your body.
This focus on the breath is often the first step in developing a meditation practice because it induces mindfulness through its awareness of the present moment.