The document discusses the differences between the preterite and imperfect tenses in Spanish. It provides examples of how the imperfect tense is used to describe ongoing or habitual past actions, mental states, and descriptions, while the preterite tense is used for single, definite past actions that interrupted the ongoing situation. It also gives an example of how the imperfect can be used to describe an ongoing action that is then interrupted by an action in the preterite tense.