Simple past: "I did it." Present perfect: "I have done it." Present perfect is used to indicate that whatever happened in the past is connected to the present, or still relevant in some way. It can also be used to indicate that it's the recent past, or that whatever happened is still happening, and you are talking about how much of it has happened. i.e.: Simple Past: "I ran a mile" Present Perfect: "I have run a mile" this could mean the speaker has run a mile so far, and is still running.