Gil Fronsdal leads a Guided Meditation on the Breath. There are 2 general ways of being with the breath in mindfulness meditation. To choose a home base.
The most common in the tradition is the sensation as the air goes into the nostrils or the rise and fall of the abdomen. When the mind wanders away, you come back to that one place, a home base.
Another whole way of being with the breath is not a specific place. It's called the breath body, all the places in the body that seem to respond to breathing like the rising of the shoulders, abdominal cavity or the back rib cage moving. It's possible to develop sensitivity to the ripple of movements or presence of energy, feeling of movement of breath, some call it the breath energy.
Today, we go to experience the breath body. The broad breath body.