The document discusses the differences between active and passive voice in sentence structure. In active voice, the subject performs the action expressed by the verb, following the structure of subject + verb + object. In passive voice, the subject receives the action expressed by the verb, following the structure of object + verb + subject. Active voice sentences are more clear and straightforward, while passive voice sentences are less clear and do not express meaning as directly. Examples are provided of converting sentences between active and passive voice.