The past perfect simple tense is used to go further back in time when we are already talking about the past. It can make it clear that something had already happened at the time we are talking about.
Past Perfect Simple Time line
We form the past perfect simple by using the auxiliary verb had and the -ed form of the regular verb (the past participle) irregular verb forms have to be learned:
“I had already done the shopping by the time she came home.”
“I was late for work, by the time I arrived the client had already left.”
The past perfect simple can be used to show how often something happened in the past.
I’d visited the city many times before.
It can also be used to express unfulfilled wishes or dreams. Sometimes called the Third Conditional.
“If I had won the lottery I would have bought a new car.” Note: If I had done something I would have done something else.