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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 most frequently used words are the meat and bones of the language, the essentials that make communication work, including I, you, go, eat, and so on. Old English developed from various Germanic languages that came to the British Isles in the second half of the first millennium AD.