It is used to describe experiences one has had in the past (and that hence influence the experience with which you speak today), changes over time, uncompleted actions, and things that have happened more than once.
15 There's no special magic with " had had ", they don't really go together as a pair anymore than " had wanted " go together. 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.
For example, what is the difference between the following two sentences: I had a bad day I had had a bad day
The first one basically just emphasizes the order of events - that you had already eaten too many chocolates before dinner, and as a result were not able to eat any more. The second one doesn't technically make it clear that you had eaten the chocolates before dinner, but then again it's really the only possible meaning in that context so the two sentences don't really have much difference in ...
grammar - had vs. had had - English Language & Usage Stack Exchange
I have come across a few sentences that contain "have had". I would like to know in what kind of situations we should use this combination.
present perfect - When is it necessary to use "have had"? - English ...
The past perfect form of have is had had (had + past participle form of have). The past perfect tense is used when we are talking about the past and want to refer back to an earlier past time.