The pluperfect tense translates as 'I had done something'. It's formed using the imperfect of 'avoir' and then a past participle. With 'avoir', the past participle only agrees if there's a direct object
j‘ avais - I had
tu avais - you had
il avait - he had
nous avions - we had
vous aviez - you had
ils avaient - they had
There are 14 verbs that use 'être' to form the pluperfect tense. It's important to note that verbs that use 'être' agree with the person who is speaking and gender.