With passive sentences, the most important thing to consider is that which was done. Who or what
did it need not be mentioned.

Las galletas fueron comidas.
The cookies were eaten.
El cielo fue illuminado por el relámpago.
The sky was lit up by the lightning.
Desafortunamente, Luis fue comido por los crocodilos.
Unfortunately, Luis was eaten by crocodiles.
The passive aboves were formed by moving the object to where the subject was,
using a form of ser, and following everything with a past
participle.
Impersonal se
The reflexive pronoun se is also used to create a passive sentences.
When used in this way it is known as an impersonal se.
A special construction is used to express accidents: impersonal se + indirect
pronoun (referring to the 'victim' of the accident) + verb.