All sentences consist of at least one subject and one verb. The tense of the verbs refer to the time the action takes place; the action can be past tense, present tense or future tense. Verbs also vary in voice. They are passive or active voice. In the active voice, the subject of the sentence is who or what is performing the action. In the passive voice, the object receives the action. It is important to keep these simple grammatical rules in mind when describing a process in passive voice.
Start your first sentence with what would be the main object of the sentence in active voice. For example, if you were trying to explain how to boil water to make tea, your first step would be: "Put water in the kettle." This is active voice. The subject, or doer of the action, is the second person imperative (You).
To change from active to passive voice, do it in two steps. First, include a form of the verb "to be" after the subject. Using the example and using a form of the verb "to be", you could write: "You were putting water in the kettle."
Second, change any sentence from active to passive voice by taking the object of the sentence and making it the subject. For example, the next step in making tea could be expressed in active voice as: "Pour the hot water into a cup." Expressed in passive voice, the sentence becomes: "The water is poured into the cup." Remember that in passive voice, the subject of the sentence, (who performs the action), is not as important as the direct object, which, in this case, is 'the water.'
Continue to express the steps of the process in the same manner. Transform the direct objects of verbs into the subjects of the sentence, in passive voice sentences. For example, your next sentence may be, "A tea bag is added to the cup of hot water."
If an active voice sentence has two objects, decide which one you want to place the emphasis on, and make that one the subject of your passive voice sentence.