Duh, we all know how to breathe, correct. However most people will overlook the basics of breathing and its effects other than sucking oxygen (amongst other things) and shoving it out.
In particular deep breathing skills, yes skills, seem to have been overlooked in education. The ability to belly breathe/diaphragmatic breathe is essential in life. Being able to stop a downward spiral between your brain and your breathe in stressful situations, such as job interviews (a situation many high school leavers will face), could mean the difference between getting that job or that partner or that deal.
How does it work? Simply, short chest based breaths are awesome for increasing energy and pumping up adrenaline which is useful when that is needed. With constant stimulus, full timetables and feeling overrun, this kind of breathing is often employed as stress increases to cope with (perceived) demands on the body and mind. Deep belly breaths on the other hand provide a more recovering breathe and generally as you get older the less you naturally do this type of breathing for whatever reason.
For a biological standpoint, the Vagus nerve provides ‘gut’ based feedback to the brain and the brain will find feedback from sensory stimulus to either excite or calm the body.
Exercise 1 : Really simple, take 10 short/sharp breaths, shallow enough to be in your chest. They should push your chest forward slightly. Notice how you feel.
Next, reset for a few breaths and then take slow deep inhales, aiming for ten seconds on the way in, a 3 second pause and the 10 seconds on the way out. Repeat this 9 more times. Again notice how you feel now.
Now I'm not gonna say to you that breath deeply and that's it. Many self-help books (with good intentions) will say that it's all you need, however there is no denying there's a time for these each of these breaths and everything on the spectrum in between!
Bonus Protip: to take this breathing stuff to the next level take a look at Scandinavian legend Wim Hof's book. He details benefits to immune system, energy levels and neurotransmitter by changing your breathing and via various breathing exercises. Highly Recommend this book on Amazon/iTunes. Wim Hof hold various records for cold water immersions and mountain climbing where he manipulates his breathing to his advantage.