The document provides instructions for changing sentences from active to passive voice in simple present and simple past tenses. It explains that the passive voice uses the form of "be" plus the past participle of the main verb and provides examples of changing active sentences like "Rita writes a letter" to passive sentences like "A letter is written by Rita" in simple present and "Rita wrote a letter" to "A letter was written by Rita" in simple past. It directs the reader to pages A-10 and A-11 for more examples of commonly used past participles.