Hi! We use the Present Perfect when the action is still in progress or it has an effect on the present. I have been learning English for two years. (I'm still learning English) I have been living / I have lived in London for a year. (I still live there) I've cut my finger. (it's bleeding, so it has an effect on the present) Past Perfect is used when an action took place before another action. Tom left the party at 9PM. Liz arrived at 10PM. --> When Liz arrived at the party, Tom had already left. Present Perfect: The ground is wet. It has been raining. (It isn't raining any more, but the ground is wet, so it has an effect on the present) Past Perfect: The ground was wet. It had been raining. (I'm telling my friend that a few days/weeks/months ago, there was rain, as a result of which the ground became wet.) Present Perfect: I have been waiting for my friend for 20 minutes. (I'm still waiting) Past Perfect: When my friend arrived at last, I had been waiting for 20 minutes. (I can't say "I have been waiting" in this case, since the waiting is already over, I'm talking about an event from the past.) Hope this helps.