This document provides information on the differences between the preterite and imperfect tenses in Spanish. It explains that 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 flow. Some examples provided include "I was writing an essay" using the imperfect and "My friend called" using the preterite to interrupt the ongoing action. The document emphasizes that the preterite "interrupts" the imperfect. It also provides a short example story using both tenses to illustrate this concept.