Basically, when you refer even further back to the past than you were referring to already. There are endless examples. Two of the simplest: She had cooked the meal long before her husband arrived home. She had had sex many times before getting married. For more get a good grammar book.

This the past perfect of 'to have' formed with HAD (the simple past tense of 'to have') and HAD (the past participle of 'to have'). Confusing, I know, because they are the same word. So, it is used in the same way you say 'I had eaten' or 'I had left'. e.g. I had a massge for the first time when I went on holiday to Hawaii or 'I HAD never HAD a massage until I went to Hawaii. e.g. I visited a friend last night and she offered me something to eat. I refused because I wasn't hungry. I HAD already HAD dinner.

Usually, 'had had' is used in causative form. Causative form is used when we do not do something ourselves, but we arrange someone else to do it for us. Let me explain it on an example: We can say "he has fixed the car", what means that he did it by himself. While using causative, it could sound like "he has had the car fixed" what means that his car has been fixed but he wasn't the one who actually mended it. When it comes to earlier mentioned "had had", the principle is the same but this time we have got past perfect: "He had organised the meeting before I came" what means that he organised this meeting by himself, but if you want to say that someone organised it for him you can use causative form and it may sound like "He had had the meeting organised before I came." I hope that my explanation exhausted this particular subject.

had had is in the past perfect the structure of past perfect is : had+ past participle have (present simple) had (past simple) had (past participle) if i had had money, i would have helped my friend.: i didnt have money, so i didnt help him we use it to express an action happened in the past before another action after i had had my breakfast, i went to school.

This is the past perfect tense: had + past participle be: had been do: had done write: had written have: had had We use it to talk about actions that happened BEFORE other actions in the past: I had already had dinner when my father arrived,