You have twenty-four ribs. Each rib has two joints where it attaches to your spine in the back and most of your ribs also attached to your sternum, or breastbone, on the front. When you breath in, your muscles lift your ribs expanding the space for your lungs which brings in air. Your ribs, ideally, lift like a bucket handle rising from lower to higher on the sides, back and front. When your spine is lined up well, nothing is in the way of these joints moving as they should. You breath easily and fully and as a result you get more oxygen in your body. The benefits of that are a mile long and include better immune function and brain function, too.
Sadly, your bones get pushed and pulled around by big things that happen to you but also by little things, too. I regularly show people how something as simple as their shoes or insoles make their bones move in such a way as to make breathing more difficult. Of course, some people prefer fashion over days filled with good full breaths, a healthy immune system and clarity of mind.
When bones get twisted in certain ways, this can lead to pain in your ribs and/or difficulty breathing. The correction, however, is quite simple.