Table salt contains anti-caking agents so shouldn't be used in an aquarium IMO. If you do use salt (Pure sea or aquarium salt), no, dont just chuck it in the tank. Desolve the required amount in some water first, then add the water to the tank as salt granules could be harmful to fish. Also, why do you need to add salt? It can help with some ailments for cure or prevention and some fish just prefer some salt. I would make sure that ALL your fish are ok with salt before going ahead and adding.
HTH
Jon