Wah How to use past perfect tense.

We use Past Perfect to describe an event or activity in the past and we want to make it clear that one event took place before another one.
The Past Perfect form is similar to Present Perfect form, except we use had instead of has,have.

Affirmative           
    I had gone to Japan.
    She had gone to Japan.

Negative
     I hadn't gone to Japan.
     She hadn't gone to Japan.

Interrogative
    Had I gone to Japan?  
    Had She gone to Japan? 

•  I arrived at the office but James had already left.                                                        (James left the office. Then I arrive there.)
•  When Helen bought a new house, she had already sold her old one.                      (Helen sold her old house. Then she bought a new house.)
•  It was great to see John again after such a long time. I hadn't seen him for ages. 
•  Scarlett cried because she had failed an exam.
•  I had never been to Oman before, so last month I decided to take a trip there. 
•  I hadn't known that bad news until I spoke to him.
•  David was not at the party because he had been sick the day before.
•  This accident happened because that yellow car had gone through a red light.

When I went back home, My wife had already gone to bed.