Going by your symptoms, most likely your system needs bled. Even if front pads/discs are worn or your rear shoes ate worn, they should take up themselves unless the self adjusters on the rear brakes aren't functioning properly. Dont trust cheap bleed kits as the bleed nipples have a tendency to pull air back in through the threads. Either use a positive pressure bleeder or get someone else to assist you by pressing the brake pedal while you back off the bleed nipples.