When should I use the present subjunctive in Spanish?

The subjunctive is used to express a number of things in Spanish. One of its most common functions is to express doubt, for example; "No pienso que sea una buena idea."  Bear in mind that subjunctive is only used with phrases like no pienso que and no creo que, since saying "creo que es una buena idea" is affirmng that it is a good idea, not doubting it. We can also use the subjunctive to express that something might happen: "Hoy es posible que terminemos la clase 10 minutos antes el timbre " Another common function is to express a wish or desire; for example, "espero que te lo pases bien" or "quiero que apruebes el examen" . This is similar also to the fact that it is used when telling someone to do something, since you are expressing a wish for them to do something: "Dile que ya vuelva a casa". A final example is that subjuntive is used to express an emotional reaction to something. It is worth learning a few examples or set phrases that you can use in a written or oral exam situation. Some examples include: Me frustra que, me da pena que, me alegra que, me extraña que, me molesta que...