The driver does exactly that, it drives the nail or staple into the medium (wood, cement, cardboard etc.). Some drivers are sold separately, some are only sold as part of a piston/driver assembly (more common). If nails are getting stuck in the nose of the gun or if it’s driving intermittently, your driver may be broken or bent and will need replacing.
This item fits the following models:
3-Nailer Combo Kit w/ Accessories
3-Nailer Combo Kit
1/4" x 50 Ft Noodle Air Hose with Coupler and Plug