.

2.  The past perfect is used to indicate an
action that was completed (finished or
"perfected") at some point in the past
before something else happened.

3.  In the past perfect, we usually two
actions that happened in the past in a
respective time between each one.
 The first action is in past perfect and the
second one is in past simple.

4.  In the past perfect we use the auxiliary
“had”, this auxiliary can combine with
the subject like this:
 I=I’d you=you’d
he=he’d she=she’d

5.  Affirmative:
Subject + “had” + Past participle
 Example:
I had been in Australia before, so I saw
Australian culture already.

6.  Negative:
Subject + “had” + not + past participle
 Example:
I had not (hadn’t) been in Australia
before, so I didn’t saw Australian culture
already.

7.  Interrogative:
“Had” + Subject + past participle
 Example:
Had you been in Australia before?
How did you know the Australian culture?