What we do is not breathing...Try this!
We live because we breathe.
There is an intricate flow of oxygen that starts from our nose to our pair of lungs, into the blood stream and then to the 30 trillion cells in our body. These cells then use this oxygen to carry out vital functions, release CO2 that is then passed out from blood to lungs to nose. All in each synchronized breath.
Our lungs are equipped with a series of bronchical tubes, the end of which are these tiny air sacs called alveoli. The alveoli are incredibly important as this is where the exchange of Oxygen and carbon dioxide takes place. And also the capillaries of the blood vessels are connected to the walls of the alveoli.
There are about 300M alveoli in both our lungs combined. Why so many? Because we have 30 trillion cells to serve with fresh oxygen every other second!
Now with all of these facts considered, relook at your breathing.
The breath you just took a second ago while you read the above lines, was most likely shallow with barely any movement in the lungs. The air probably went in 10 - 20% and came out without any act. You might have even held your breath as you were focused on reading.
And now take a deep breath that goes in to fill the edges of your lungs to all the 300M+ alveoli, that go in to now supply fresh oxygen to all your cells!
Feel the difference?
I am sure you did :)
So, expand your chest, push your diaphragm down, fill your lungs up, your stomach up, your shoulders up and Take a deep breath!