Diaphragmatic breathing (also known as belly breathing) is helpful for regulating the nervous system, calming stress responses, and improving physical and emotional health. 
 
By shifting the body out of "fight-or-flight" mode (sympathetic) and into "rest-and-digest" mode (parasympathetic), access to activating the vagus nerve can start to add in relaxing muscles and held patterns, and regulating digestion. 
 
When there is a sense of safety in the body and there's no perceivable threat this type of breathing practiced consistently — with no agenda to "arrive" anywhere perfectly — we can start to invite a curious interoceptive awareness. This awareness can slowly and gently start to make it easier to recognize emotions before they overwhelm.
 
There's no need to get anything "right" here, just simply allowing what's your current capacity to be accessed. 
 
Thank you for practicing, and remember you can return to your breath whenever you choose.