"Have done" is called present perfect tense and "Had done" is called past perfect tense. Here are examples: "I have lived here for there months." : Meaning "I" started living here three months ago, and continue until now. "He have done five 20-page term papers." : Meaning he did five 20-page term papers so far. ( the number of paper is emphasized); this sentence also describes an action that happened before NOW without exact date. "I had been there when she came." : Meaning I was there BEFORE she did. So, tips are: 1, "have done" doesn't require a certain date an action happened. It either shows the recently done action or emphasizes the result of an action. 2, "had done" requires the certain date because it describes an action happened BEFORE that date. Hope this helps!