Difference between PQP and passe compose

PQP - The past perfect, or pluperfect, is used to indicate an action in the past that occurred before another action in the past.

So an action that occurred before is shown using PQP and then the Passe compose is used to highlight the next action. All actions have occurred in the past. 

The PQP is conjugated as  the imparfait of avoir or etre + past participle of the main verb

• When the auxiliary verb is être, the past participle must agree with the subject
• When the auxiliary verb is avoir, the past participle may have to agree with its direct object

for example, I went for shopping in the morning. (action in past) and before that , I cleaned the house (an action that occurred before, also in the past). 

So, the sentence to highlight both actions can be written as -  J'ai fait du shopping le matin, j'avais deja nettoyé la maison.

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