Answer:
The nervous system sends impulses starting from the brain down the spinal cord (the central nervous sytem) and then out to the perhipreal nervous system which goes thoughout the whole body. These impulses go to every other body system and tell them how and when to work.
It is much more complicated than that but I'm only 8th grade and i had to make a poster for it in 3 days so i didnt learn a whole lot about it