The past perfect tense is used to express action completed in the past:
"She had eaten is an example of the tense."
The past perfect tense represents action that occurs BEFORE another past action:
"My boss had gone before I had the chance to see him."
How to Form the Past Perfect Tense
The past perfect tense uses had + the past participle of the main verb
"She had never tried surfing before she visited Australia."