The Past Perfect Subjunctive Tense is a past tense meaning I had done something.  It is formed by using the past subjunctive tense of the verb HABER (to have done something ) + Past Participle.  

The Past Participle is formed by removing the AR from the infinitive and adding ADO e.g. Hubiera hablado – I had spoken.

The Past Participle is formed by removing the ER or IR from the infinitive and adding IDO e.g. Hubiera comido – I had eaten.