Based on the formation of stative passive (Zustandspassiv) that you already know, I will construct examples with:
[patient] → der Hund
[preposition] → von
[agent] → die Frau
[past participle of verb] → gefüttert (infinitive: füttern)
Perfect Passive example:
[patient] ist [preposition] [agent] [past participle of verb] worden
Der Hund ist von der Frau gefüttert worden.
(active voice, perfect: Die Frau hat den Hund gefüttert.)
Past Perfect Passive example:
[patient] war [preposition] [agent] [past participle of verb] worden
Der Hund war von der Frau gefüttert worden.
(active voice, past perfect: Die Frau hatte den Hund gefüttert.)
The difference between both examples is the tense (perfect/past perfect or Perfekt/Plusquamperfekt), which is denoted by the different forms of sein (ist/war).
These difference signals different meanings, but this is comparable to the differences between perfect and past perfect in active voice. In both sentences, the feeding is done already (hence the perfect tense), but the "reference time point" differs (present vs. past).
In perfect tense, the "reference time point" is the speaker's present tense (now).
The speaker notices that now, the dog has been fed by the woman. (in active voice: The woman has fed the dog.)
In past perfect, the "reference time point" is the speaker's past. For example, the speaker tells you, that when he came home yesterday, the dog had been fed by the woman. (in active voice: The woman had fed the dog.)