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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 .
The following helping verbs are used in these tenses: have, has, had, will, shall. Use the present perfect verb tense to indicate an action that has recently ended or that began in the past and is continuing into the present. Use has or have and the past participle of the main verb.