ana … pana … sati

breathe in … breath out … be here now

The center of our practice is the breath.

Mindfulness of breathing meditation is merely focusing attention on breathing in and breathing out.

To help focus the attention, the meditator can make a mental note “in” while breathing in and “out” while breathing out.

We don’t try to control the rate, length, or depth of breathing in any way. We just maintain mindful awareness on the natural rhythm of breath as it happens in the present moment.

Breathing in, i see myself as clear water.
Breathing out, i accept things as they are.
Thich Nhat Hanh
Breath is a naturally occurring meditation object which is always there with us as we continue to breathe from the time we are born until our death. It is also a good reflection of the state of our body, mind, and the emotions at any given time.
Dr. Ari Ubeysekara ref

The Buddha gave several teachings on the practice of anapanasati. The two main ones are the anapanasai sutta and the satipatthana sutta.

More about meditation.