You should look for exercises to practice these, as an explanation will not be enough. I've given the names of the grammar forms in parentheses, so you can search for them. "Did" (simple past) and "had done" (past perfect) are used when you talk about past events. "Have done" (present perfect) is about the present. To be exact, we use a past event to describe the present. This grammar is taught at elementary level, so you really can't ignore present perfect if it confuses you.

Peachey is right... if you don't understand the differences between these tenses, you need to go learn them and master them sooner rather than later. This is important and fundamental. However, I will attempt a short tutorial to get you started. (please forgive any errors in my Chinese, I have only a rudimentary knowledge of Mandarin) In European languages, past and present perfect are two different verb tenses and it's pretty easy to map past, present and present perfect tenses to European languages. It's harder to differentiate "I did" and "I have done" for a Chinese speaker because they translate to more or less the same thing in Chinese. "did", "have done" and "had done" are all verb tenses of the verb "to do" "I did my homework" "I have done my homework" (really not much difference in meaning from "I did my homework" except for being a bit more emphatic) 你的功课做了 This week, I did my homework before dinner every day. This week, I have done my homework before dinner every day. (once again, not much difference except maybe one of emphasis) 这个星期，我每天都做晚饭前功课做了 I had done my homework already when you arrived 你到来的时候, 我的功课已经做完了 NOTE: The important point about "had done" (past perfect tense) is that the action comes before another action in the sentence. In this case, "(my) doing the homework" came before "you arrived". Hope this helps