i have seen my fleet points and my research points and my building points.
now how does it work exactly? such as how many points do you get per ship or per building? and does defences give you points? if not why not?

Points depend on how much you have spent for the ship, building, research or defense. Yes you also get points on the defense. It just isn't shown on the overview.
You can look at your points (General, Fleet, Research, Building, Defense) on the ranking page.
You might wonder why you have different fleet points on the overview and the ranking. The fleet ranking only shows the number of ships not the actual points.