This car probably needs a new master cylinder like Gary said, but you could try bleeding them first at least. Adding fluid will do nothing to fix the problem.
And crawl under and check the insides of all your tires, you are looking for signs of leaking brake fluid. If you find any pull the wheel off and inspect the caliper or wheel cylinder(if there's drums on the rear). The caliper/cylinder would be leaking badly and need replacement. And bleeding
