I've been wondering, when would it be appropriate to use haben or hatten with a past participle?
What exactly is the difference between, "Ich habe es gemacht," and, "Ich hatte es gemacht"? Would the English equivalents be, "I have done it, or"I did it." and, "I had done it"?
That is correct. 'habe' is used for the perfekt tense. Just remember that you don't always have to use 'have' in the English translation. 'hatte' is the form for the past perfect and refers to a time in the past prior to a more recent time in the past.