The Pronoun se
  Se in an unstressed third-person pronoun that serves a variety of grammatical functions.  
  • Reflexive se is part of a full conjugation. (See reflexive). It can appear in either with either a third-person singular or third-person plural verb:
    • Norma se levanta a las seis, y sus hijas se levantan a las siete y media.
  • Impersonal se appears only with third-person singular verb forms. This structure describes actions or states involving unspecified persons.
    • Los sábados se va al cine o se limpia la casa.
      • On Saturdays one goes to the movies or cleans the house.
    • ¿Qué se hace por aquí cuando llueve?
      • What does one do around here when it rains?
  • It cannot be used with a third-person reflexive verb form, since se will already be present; the pronoun uno/a can be used instead to represent the non-specific persons performing action:
    • En las residencias estudiantiles, uno se levanta después de las diez los sábados por la mañana.
      • In the dorms, one gets up after ten on Saturday mornings.
  Passive se appears with third-person singular and plural verb forms to express actions in the passive; the person doing the actions are not specified.  
  • The verb agrees with the subject in number (singular or plural); the subject most often follows verb:
    • Se venden más de mil copias al día de ese periódico.
      • More than one hundred copies of that newspaper are sold per day.
    • Se oye música en el parque.
      • Music is heard in the park.
  • Exception: When the noun following the verb noun is preceded by the personal a, the verb must be singular, regardless of whether the noun is singular or plural:
    • Se critica a ese político / Se critica a esos políticos.
      • That politician is criticized / Those politicians are criticized.
  • Se is used in place of indirect object pronouns le and les when a direct object pronoun follows:
    • Le explico la gramática a Juan; Le→Se la explico después de la clase.
  • See indirect objects.
  • Se is combined with an indirect object pronoun to describe unexpected or accidental events:
    • A mi hermana se le ocurrió una idea brillante.
  • Click here for more examples.