The past participle is the '-ed' form of the verb, like 'forced', 'walked' and 'asked' (except for irregular verbs, whose past participles are... irregular (meaning 'not -ed'), like 'spoken', 'bitten', etc.)
The past perfect tense is one finite verb form that uses the past participle: 'had forced', 'had spoken', 'had bitten'. The present perfect tense also uses the past participle: 'have/has walked', etc.
And we also use that form in the passive voice: 'be asked', 'be carried'.
- For Teachers