This document discusses the differences between using the present perfect and past simple tenses in English. It provides examples of when to use each tense, such as using the present perfect for unfinished or ongoing actions and the past simple for finished or definite past time actions. It also lists time expressions that are commonly used with each tense, such as "for" and "since" with the present perfect and "yesterday" and "last week" with the past simple. Finally, it provides exercises for the reader to practice using these tenses in sentences.