Past perfect

The Past Perfect tense in English is composed of two parts: the past tense of the verb to have (had) + the past participle of the main verb.

Subject	had	past participle
We	had	decided...
Affirmative
She	had	given.
Negative
We	hadn't	asked.
Interrogative
Had	they	arrived?
Interrogative negative
Hadn't	you	finished?

Example: to decide, Past perfect

Affirmative	Negative	Interrogative
I had decided	I hadn't decided	Had I decided?
You had decided	You hadn't decided	Had you decided?
He, she, it had decided	He hadn't decided	Had she decided?
We had decided	We hadn't decided	Had we decided?
You had decided	You hadn't decided	Had you decided?
They had decided	They hadn't decided	Had they decided?

Past perfect, function

The past perfect refers to a time earlier than before now. It is used to make it clear that one event happened before another in the past. It does not matter which event is mentioned first - the tense makes it clear which one happened first.
In these examples, Event A is the first or earliest event, Event B is the second or latest event:

Event A	Event B
John had gone out	when I arrived in the office.
I had saved my document	before the computer crashed.
When they arrived	we had already started cooking
He was very tired	because he hadn't slept well.

Past perfect + just

'Just' is used with the past perfect to refer to an event that was only a short time earlier than before now, e.g.
a. The train had just left when I arrived at the station.
b. She had just left the room when the police arrived.
c. I had just put the washing out when it started to rain.