What's the difference between past perfect and past participle? Examples are helpful, but an explanation would be better.
Past Perfect is a tense while Past Participle is a verb form. See explanation.
Past Perfect is one of English past tenses used to indicate that one of 2 past actions took place before another like in a sentence:
I had written my homework before I went for a walk.
Form had written suggests that one action (writing homework) took place earlier than the other (going for a walk).
Past Participle is one of the verb forms (usually the third form in a table of irregular verbs). It is used in perfect tenses, passive voice, etc.
Past participle of the verb to write is written. It can be used in:
Past Perfect as in the example above,
Passive Voice: This letter was written by John.