The document discusses the use of the present perfect tense in English with various time expressions including "just, already, yet, for, and since." It provides examples of how these words are used with the present perfect to talk about actions that began in the past but have relevance to the present. The key uses are: just means a short time ago, already means sooner than expected, yet is used in questions or negatives, for indicates duration, and since indicates a starting time point.