The simplest way to explain the difference is that perfect passive participle is taking a verb and turning it into an adjective. For example: take the verb "to bite." The perfect passive participle of "bite" is "bitten." i.e. the child, having been bitten. Alternatively, the perfect active participle of "bite" would look like "having bitten." i.e. The child, having bitten his brother, was punished. The same thing applies in latin. Let me know if you want me to explain further.

Is this a question about Latin grammar or English grammar? You have posted it as an "English" question.