At the beginning of breath awareness practice we can feel our attention is either with the breath or distracted. As we deepen out faith and dedication to mindfulness of breathing we learn to breath in and breath out in all conditions. The breath becomes a sanctuary to accompany us in all conditions.
In the detailed description of the 16 steps of anapanasati (mindfulness of breathing) the first 12 steps develop samadhi (concentration) as a basis for the last four steps (13-16) of insight practice. These are using in and out breathing to become sensitive to impermanence (anicca), and from impermanence to releasing the agitation (viraga) from trying to find security in a fluid and fluctuating world. The second to last step in relaxing into the completeness and thoroughness of endings (nirodha), as a support to the last step of fully letting go.
Let your body be present and also relaxed. As you let go, feel how the Earth completely supports you. Let the heart be soft to receive whatever arises with compassion. Begin to notice how the body is breathing itself, exchanging air with the leaves of the trees around you and with the breath of every other living being on Earth—we share this atmosphere.