When to use the passive:

when you want to focus on the person or thing affected by the action, or the action itself;

when it is not important who or what did the action;

when you want to be impersonal or more formal, as in most forms of academic writing.

Form the passive by:

turning the object of the active sentence into the subject of the passive sentence

changing the verb to a passive form by adding the appropriate form of the verb 'to be' and the past participle of the main verb.

Warning:
Some faculties or schools within faculties discourage the use of the passive voice. Check on your department's protocol in regard to the passive voice before submitting your work.