Structure: subject + had + past participle form of the verb

• They had come.
• She had written a novel.
• I had waited for two hours.
• He had left early.

In the past perfect tense we make the negative forms by putting ‘not’ after had.

• They had not arrived. 
• She had not passed the test.
• It had not stopped raining.
• We had not received the invite.

The past perfect tense is used to indicate that an action had been completed before another action took place.

• The train had left before I reached the station.
• The rain had stopped when he went out of the house.
• She had finished her studies before she went to the US.

Note that the past perfect is used to talk about the earlier past action whereas the simple past is used to talk about the later past action.

We do not use the past perfect tense to simply state that something happened sometime ago. That meaning is expressed with the simple past tense.

• I met him yesterday. (NOT I had met him yesterday.)
• She left ten minutes ago. (NOT She had left ten minutes ago.)