Form an active sentence. Some examples include "Él observa los pajaros" and "Ella lee los livros."
Identify the object receiving the action, the subject doing the action, the verb and the verb tense. In the previous example, the objects receiving the actions are "los pajaros" and "los livros." The subjects doing the action are "él" and "ella." The verbs are observar and leer, and both are in the present tense.
Change the sentence so that the direct object is the subject. In the previous examples, the subjects would now be "los pajaros" and "los livros."
Conjugate the verb "ser" to the present tense, because the verbs are in the present tense. If the original sentence was in the past, the future or the subjunctive, you would conjugate ser appropriately.
Conjugate both verbs to the past participle, or participio pasado. In this case, it would be "observado" and "leído."
Add the word "por" and the subject after the verb. So, the final sentences will read "Los pajaros son observado por él" and "Los livros son leído por ella."