Past Perfect is used to express an action that occurred before another one in the past. For instance, check this example:
When
I arrived to the station,
the train had already left.
recent action oldest action
There are time expressions that are used with this tenses:
for, since, just, when, never, until,etc.
Past Perfect Continuous is similar to Past Perfect, but it gives emphasis to the duration of the action. You might have 1) time expressions that help you to understand that the action is long, or 2) you have the action itself which is long, for example go for a walk, read a book, drive a car, etc.
There are time expressions that appear with this verb tense:
for, since, how long
Example:
He
had been driving for two hours when the police caught him.
In this link you find the explanation and short exercises:
http://www.monash.edu.au/lls/llonline/grammar/engineering/tense/4.xml
