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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 .
verb (used with object), present singular 1st person have, 2nd have or (Archaic) hast, 3rd has or (Archaic) hath, present plural have; past singular 1st person had, 2nd had or (Archaic) hadst or haddest, 3rd had, past plural had; past participle had; present participle having. 1. to possess; own; hold for use; contain: