The French subjunctive tense/mood is required when expressing cases of doubt, necessity or emotion. For example, "Je veux que tu gagnes" (I hope that you win), "Il faut que tu sois à l'heure" (You need to be on time/It is necessary that you're on time) and "J'ai peur qu'il ne vienne pas" (I'm afraid that he won't come) are all examples of when the subjunctive is required. However, it is important that you remember that verb constructions ending with 'que' that relate to time e.g. "dès que", "après que", and "tandis que" are followed by the INDICATIVE and not the subjunctive, even though they too end with 'que'.