The passive voice in Spanish can only be made in senteces that have DIRECT OBJECT. (transitives) Fist of all, you must know very well the SER and ESTAR verbs in spanish YO SOY YO ESTOY TU ERES TU ESTÁS EL / ELLA ES EL / ELLA ESTÁ NOSOTROS SOMOS NOSOTROS ESTAMOS VOSOTROS SOIS VOSOTROS ESTÁIS ELLOS SON ELLOS ESTÁN their infinitive form is SER and ESTAR, IT's necessary to know it because with modals verbs and auxiliary verbs you must use SER or ESTAR. In English It is BE Mary eats an Apple ----> an Apple is the DIRECT OBJECT In addition, you must know the participle verbs in spanish: eaten ----> comido driven-----> conducido forgotten-----> olvidado...etc. The structure is : DIRECT OBJECT + SER / ESTAR verb + PARTICIPLE verb + POR + AGENT VERY IMPORTANT: The subject in active is the agent in passive Mary eats an apple Maria come una manzana An Apple is eaten by Mary Una manzana es comida por Maria Mary ate an apple Maria comió una manzana an Apple was eaten by Mary una manzana fue comida por María Mary is eating an apple María está comiendo una manzana An Apple is being eaten by Mary Una manzana está siendo comida por María Mary has eaten an apple María ha comido una manzana an Apple has been eaten by Mary Una manzana ha sido comida por María

It is like English. I am going to try explain you in "Spanglish! jaja: In a sentence, you should apreciate the verbal form of the main verb. EX: "Yo compro flores" (the verb is "compro") the verb is a present so you must use, in the passive voice, the verb "SER" in the same verbal form (present) and you add the parcitiple of the verb that you have in the active sentence, making the concordance with the new subject. EX: COMPRADAS (because the word "flores" is femenin and plural. "Las flores SON COMPRADAS por mí" To resume, the structure is: Sujeto paciente +verbo SER en la forma correspondiente + PARTICIPIO DEL VERBO PRINCIPAL (en activa) + Complemento agente (POR... mí, ti, ellos...). Be careful because not all setences could transformate in a pasiva. Just what are transitive setences. I hope it could help you.

Mary had eaten an Apple María había comido una manzana an Apple had been eaten by Mary una manzana había sido comida por María Mary will eat an Apple María comerá una manzana an Apple will be eaten by Mary una manzana será comida por María Mary is going to eaten an Apple María va a comer una manzana an Apple is going to be eaten Una manzana va a SER comida por María Mary must eat an Apple María debe comer una manzana an Apple must be eaten by Mary una manzana debe SER comida por María Mary can eat an Apple María puede comer una manzana an Apple can be eaten by Mary Una manzana puede SER comida por María Mary should eat an Apple María debería comer una manzana an Apple should be eaten by Mary una manzana debería SER comida por María ....etc once you have understand it, you must learn the PERSONAL AND IMPERSONAL PASSIVE IMPERSONAL: It's said that Jane is in hospital --- se dice que Jane está en el hospital (it is often used) IMPERSONAL: Jane is said to be in hospital ----de Jane se dice que está en el hospital..(está no es usada en spanish, Don't use it,) I hope you can understand better the passive voice in spanish! ;)

How is passive voice constructed in spanish?

is better write it in English