Yoga sutra 1.34
Pracchardana-vidharanabhyam vā prāṇasya
A peaceful mind can also result from exhaling the breath and holding the breath
In this sutra and the sections that follow, Patanjali outlines techniques to calm the mind and centre yourself.
The first such technique is breathwork, with emphasis on exhaling your breath and holding your breath. It has to be done in mild way (and for this reason the Prana Vashya Yoga™ sun salutation incorporates this breathing technique). This is the first step towards Pranayama. Pranayama is covered in detail in the following blog article: So what is pranayama? (pranavashyauk.com) and requires a competent teacher.
Damian Cadman-Jones is an authorised teacher of Prana Vashya Yoga™