The document discusses the differences between the past simple and past continuous tenses. The past simple is used for actions that started and finished in the past or repeated actions. The past continuous describes actions that were ongoing or in progress at a time in the past. It is used when talking about two simultaneous past actions, one ongoing and one starting or finishing. Examples are provided to illustrate when to use each tense, including sentences using "when" or "while" to connect two actions, one in the past simple and one in the past continuous.