in every complete sentence, there will be a subject and a verb.

when writing in passive voice, the verb is acted upon by the subject, and when writing in active voice, the subjects acts out the verb.

i am have discussed the use of passive and active voice in writing.

the use of active and passive voice in writing was discussed by me.

or, as i found was elegantly taught in the university of north carolina,

why was the road crossed by the chicken?