In Spanish, there are two main groups of verbs, indicativo and subjuntivo. It's very simple. In order to understand this, imagine I am holding two hands, one in each hand. In the left bag I am going to put the "Indicativo" tenses, that is, the present simple, the preterite, the imperfect, the future and conditional , the present perfect, the pluperfect, the future and conditional perfect. In the right bag I am going to put the subjunctive tenses: the present, present perfect subjunctive, imperfect subjunctive and pluperfect subjunctive. What is the difference between both? Easy. the tenses on the left bag refer to facts, things that have happened, statements or decisions that have been made.

On the contrary, the right bag contains tenses with which Spanih express everything that is not a fact in language: desires, opinions, speculations about the future and the past, hypothetical situations, commands, recommendations, suggestions or necessities. For instance, a typical example of a subjuntive sentence is one that begins with the expression "ojala" (I wish), which is followed by the relative pronoun (usually it is not said) and a verb in the subjunctive: "Ojala llueva esta tarde" (I wish it rains this afternoon). In this sentence, there is a main clause formed by "ojala" and a subordinate clause formed by the subjunctive verb.

It is easier to learn when to use the subjunctive if you think first of a "trigger" expression like "ojala", "espero que" (I hope that"),, "quiero que" (I want somebody to) or "cuando" to refer to the future, as in cuando llegues, llamame, When you arrive, call me". In this sentence, the verb "llegues" is the subjunctive form of "llegar" to arrive. Notice that if the verb in the main clause is in the past, the verb in the subordinate clause must also be in the past: "queria que Juan viniera a la fiesta", "I wanted Juan to come to the party".