It is very simple,Jarvis.Past Perfect is the "past of the past" that means it is used for a past action that happened BEFORE ANOTHER action in the past.

For example "After he had eaten his breakfast,he went to school."

First action he ate breakfast

Second action he went to school.

First action will be past perfect,second action (later on) will be past simple.

Ruthi you are a great person, and you help everyone with your knowledge, thank you for this! SALUDOS from Chile

It is not so simple, Ruti.

he had eaten his breakfast - is the Past Perfect tense, but the Past Perfect Continuous tense is <em>he had been eating his breakfast.</em>

<em></em>He had been eating his breakfast for ten minutes when she called him.