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So don't worry so much about how to use  had had  as a unit of grammar, they will come together naturally when you want to express the verb ' to have ' in the past perfect. Let's consider a different verb for a moment like  to want .
for example she has gone to school she has been to america though they belong to the same tense their use is different from each other they are used in different contexts and cannot be used in each other s placemany people do not know about their different uses and use them incorrectlyhen you use been in the sentence he has been to america it denotes that he went to america and after some time came back he is not in america anymore another example can describe it better he has gone to india and he has been to india twice both sentences cannot be interchanged