Take 5 long breaths in and slow your exhale. Begin your count on the exhale and it will automatically slow your inhale. This equals about 30 seconds of deep breathing, which engages the relaxation response through your endocrine system. This response counteracts the stress response and they cannot exist at the same time.
Your breath controls your mind. It does this by impacting your heart rate, known as heart rate variability. As you breathe you are changing and shifting your nervous system between parasympathetic (rest/digest) and sympathetic (fight/flight) all day long. By taking control of your breath, you take control of your heart rate, when you do this your brain gets the signal that things are ok.
This builds self confidence by allowing you choices in each moment. Over time you learn that you have skills to figure things out, even when you do not like any of the choices in front of you.
Choices allow you to respond rather than react, thus you are more regulated in every interaction throughout your day, doing just what is needed in each moment. No more, no less.