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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 .
Have can also be used as a main verb. In this case it is followed by an object. As a main verb, have is used to talk about our possessions, relations, experiences etc. 1  I have a sister. 2  She has a car. 3  He has a nice job.