The document discusses various tenses used to express actions or states that are completed or ongoing in the past. It explains the simple past tense is used to denote an action completed in the past with no reference to time. The past perfect tense indicates an action completed before another past action. The past continuous tense is used to show an ongoing action in the past. The past perfect continuous tense expresses an action that started and finished in the past, with reference to the duration.