A grille is a metal grate used as a decorative and protective covering, especially for a car or a fireplace.
You grind something by breaking parts of it off with friction. Metal or wood can be ground down by running a very rough surface over it, such as a grinding disc or sandpaper. Grinding will gradually change the shape of the thing being ground as the outer layer is removed.
You grind herbs and spices in a mortar and pestle by crushing them against the inside of the bowl.