when can i use "had + been + verb+ed " and "had+ verb+ed"

read active & passive voice.. ex: I had eaten mango: (had+V3) (its active voice, here "I" is important. means the person who is eating is imp. we r not giving importance to object which is mango) Mango had been eaten: (had+been+V3) (its passive voice, here object mango is important, we r not giving importance to person who is eating it) Mango had been eaten.

Past perfect tense : sub + had + v3. This tense is used to show that something happened before another action in the past. Ex..The train had already left the station before he went there. In the above sentence train leaving the station happened before he went there. So before happened action is mentioned in past perfect and after happened past action is mentioned in simple past. Passive form of Past perfect tense : object + had + been + v3 Here we give priority to the object as we don't know or don't want to mention subject. Ex..My work had been done before you came here. In the above sentence we gave priority to the object and not mentioning by whom the work is done.