This document discusses the use of the present perfect tense in English to talk about unfinished or ongoing actions, actions that happened recently, and recent past experiences when time is not specified. It explains that "since" is used with a specific time in the past while "for" is used to indicate a period of time. Examples are given showing how to use "just", "already", and "yet" with the present perfect tense. The key difference between using the present perfect and past simple is noted - when a specific time in the past is mentioned, use the past simple tense.