The document discusses the simple past tense, which is used to express activities completed in the past. It provides examples of affirmative, negative, and interrogative sentences using the simple past tense. Key words that are used with the simple past tense include yesterday, last week, last night, and other designations of past time. A variety of examples of simple past tense verbs are given, such as swam, went, ate, built, bought, and drove.