The document discusses the difference between the present perfect and simple past tenses. The present perfect is used for actions that are not completed or when the time is unspecified, while the simple past is used for completed actions or when the specific time is mentioned. Examples are provided to illustrate when to use each tense, such as with unfinished time periods or durations (present perfect) versus finished time periods or mentioning a specific past time (simple past). Links are also included for additional practice with these tenses.