Passive Voice is the thing or person becomes the subject of the sentence.
Formula Active to Passive Voice:
Active Voice: S + V + O
Passive Voice: O + V + S
For example:
Active voice: She prepares dinner.
In active voice 'she' as subject (S), 'prepares' as verb (V), and 'Dinner' as Object (O)
Passive, we can turn around the O from back into the front of sentence.
Passive voice: The dinner is prepared by her.
'The dinner' as subject (S), 'is prepared' as Verb (V), and 'by her' as object (O)