What's the functions of each individual structure in a cell's nucleus?

Nucleus - the control center of each cell. It regulates, monitors and organizes the whole cell

Its much more easier if we compare it with the brain since the act similarly.

As the head organ in the body which controls, monitors, supervises and influences the different organ system in the body and of the individual - characteristics, personality, traits, cognition, perception, intelligence, sensation and motor responses. The brain controls the organ systems (organelles) on the needed organismic activities such as digestion, respiration, circulation, sensation and etc.