I'm presuming that you want to ask this: "How do you say 'Shut up!' in French?" [ 'Shut up' doesn't mean anything in French...it's an English phrase. You are asking for a translation]. I'm not a native speaker, but I'd use 'Tais-toi!' as a reasonably direct way of telling someone to be quiet. A ruder, more colloquial alternative would be 'Ta gueule!'.