It says that slot number 5 is for nades but my PC does not recognize slot 5 for any weapon. How do I throw a nade?
Grenades in Last Light are used like any other throwables. Use the "WEAPONS INVENTORY" button to choose the throwable you want, then use the "SECONDARY" button to use it. If you are playing on Ranger Hardcore difficulty you might need to switch throwables by sound since the hud is disabled.