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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 .
(main verb: written; auxiliary verb: has). We have been stranded for six days. (main verb: been; auxiliary verb: have). In Spanish, the present perfect tense is formed by using the present tense of the auxiliary verb haber with the past participle.