Indicative present perfect / Basic rules

Present perfect tense of the indicative is used to describe an action or fact that has already occurred at the time of the sentence:
examples : j'ai rigolé, il s'est drogué, nous avons travaillé (I laughed, he was drugged, we worked ...)

It is a compound tense, ie. avoir or être auxiliary (to have or to be) at present tense 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)