What does Rising during bread making mean? What happens during this stage?

Rising is when the dough is placed in a warm place and allowed to double in volume. Usually a dough goes through two rising periods, the first after mixing and the second after shaping,
The first rising (proofing) improves the flavour and texture of bread. From the yeast's fermentation, it takes time to accumulate a volume of carbon dioxide gas during the risings, strong enough to stretch a bread dough and to hold it high. On the outside, the dough expands like a balloon, called rising but inside the dough a number of things are happening too.
During rising, the gluten, begins to repair and pull together, which also makes the bread dough easier to work with. Yeast, feeds on the starches in the flour and doubles in number. All of these by-products are important when making bread: the carbon dioxide causes the air bubbles created in the dough to expand or rise, the alcohol contributes to the bread's flavour, and an organic acid glutamathione, relaxes the dough and gives it more elasticity. This allows it to absorb surface water, making the dough less sticky.
Shaping takes place after the dough has doubled in size from its first rising and is punched down (kneaded). Afterwards, a second rise takes place for the dough to produce more carbon dioxide and alcohol for better texture and taste. Shaping also forms the dough for an optimal oven-spring or rise when placed in an oven to bake.