This is not a particularly easy area of language and is complicated in Spanish by the fact that it has two verbs for "to be" and the "reflexive" alternative to avoid the pure Passive form. Like the Subjunctive, The Passive is a mood and the verb "to be" can be in any tense. Here are some succinct notes to take you through it followed by some exercises (it is also on slide 66 of the tenses overview here but the reflexive form is not covered).