Indicative pluperfect / Basic rules

Incative pluperfect is used to describe an action that happens before a past action :
examples : elle me raconta qu'elle avait rigolé, il m'avoua qu'il s'était drogué... (She told me she had laughed, he confessed that he had drugged ...)

It is a compound tense, ie. avoir or être auxiliary (to have or to be) at indicwtiveimperct followed by the past participle of the verb.

When verb être (to be) is used as auxiliary, past participle agrees with the subject.
Where avoir (to have) is used ad auxiliary, past participle does not agree with the subject but with object of the sentense if it's before verb (except in special cases)