Upasaka Sirinath, interested,
by "playing", using, testing out kinds of breath and perceptions, feelings, touches around it, one clams the body fabrications together with the related mind fabrications till joy within the body, and related calming of domanassa is experienced. Dwelling right there one, dwells in the first Jhana.
But such can not be done when still attached to home, the world, to the senses or when there is much remorse by not having taken the precepts by heart. If one is still a stingy person, or one without gratitude, wrong views, such as well is a total blocking hindrance. So a lot of merits in advanced are required and will give the causes to do such meditation.
Some generous recitations and advises in other words by Bhante Thanissaro Thera from Mindfulness of the Body:
The fourth step is, in the Buddha’s words, to calm bodily fabrication. You tell yourself, every time you breathe in, “I will breathe in calming bodily fabrication.” When you breathe out, you tell yourself, “I will breathe out calming bodily fabrication.” The word “fabrication,” or saṅkhāra, here has to do with what you are intentionally doing in the present moment to shape your experience. The term “bodily fabrication” means the breath, because there is an element of intention in the way you breathe, and this element of intention has an effect on the way you experience your body as a whole. As you begin to see the effect that the breath has on the whole body, you take advantage of the fact that you have the choice to make that effect more calming throughout the body.
Now, as he says elsewhere, one good way to calm the body is first to develop a sense of rapture—an energizing sense of fullness in the body. Then, when the body has been nourished by rapture, it will calm down, not from being forced to be calm, but because it feels naturally inclined to grow calm from that sense of fullness. So “calming bodily fabrication” can sometimes mean that you use the way you breathe to develop a sense of rapture in the body before you try calming it down. The sense of fullness and calm will then help you to stay more firmly in the present.
That's by the way also a tool how to prevent oneself in daily live, being touched by thing causing annoying or greed. By focusing on the breath for some deep breath in breath out one prevents oneself to act again foolish having uprooted the causes for foolish reactions within oneself.
This is why wise say "as soon as forgetting the breath one is like an orphan and acts in very foolish ways". Take care of you by not staying a poor orphan!
(Note that this is not given for trade, exchange, stacks, entertainment and akusala deeds, but as a share of merits and to continue such for release)