Without breath, we are without life.

When was the last time you paid attention to your breathing? 

Start by taking a deep breath in front of a mirror.  What did you see?
 
If you noticed that your upper chest and shoulders moved, then like most people, you are considered a chest breather.  This means you are only using the the top of your lungs to breathe, resulting in less oxygen intake.  You may also experience constant tension or discomfort in your upper back and neck as the accessory respiration muscles are overworked (upper trapezius, sternoclidomastoid and Scalene muscles) and never have the chance to relax.  It also means that you are not using the most important muscle responsible for respiration: the diaphragm
In Yoga the act of controlled diaphragm breathing is called _Pranayama_
In Sanskrit Prana means 'life' or nourishment
Yama means 'control' or discipline
Ayama means 'expansion' or 'extension'
When you practice Pranayama breathing you are nourishing your mind, body and spirit; improving the function of your diaphragm; demonstrating control of your body and developing breath awareness.
 
Try the following exercise to help you connect with your breath:
 
Lay down on your back with your knees bent.
Place your hands on your upper chest and belly
Take a few cleansing breaths to focus your mind and then when you are ready, try to inhale into your abdomen first
then notice as you inhale how your ribs expand and chest may rise
As you exhale draw your bellybutton towards the floor
Inhale 4 counts and exhale 4 counts.
Repeat this cycle 4 or 5 times.
 
Once you have mastered belly breathing while lying down, try it on your  hands and knees.  Then progress to a comfortable cross-legged position (Sukhasana/easy pose). 

It may feel awkward or challenging to breathe this way at first, but the more you practice, the easier it will become.