The verbs have five basic forms: the base, - S, -ing, past, and past participle forms.
The past participles for regular verbs are the same as their past forms (look-looked-looked and study-studied-studied).
For irregular verbs, the past and past participle forms are different (for example, be- was/were-been and go-went gone).
The past participle is commonly used in several situations:
1.Past participles are used as part of the present and past perfect tenses (both "regular" and continuous).
The non-continuous present perfect tense uses has or have + the past participle; the present perfect continuous tense uses has or have + been (the pastparticiple of BE) + the - ing form of the main verb.
He has (He's) taken a vacation. /
He has (He's) been taking a vacation.
The non-continuous past perfect tense uses had + the past participle; the past perfect continuous tense uses had + been + the - ing form of the main verb.
She had (She'd) lived here for 10 years when I met her.
She had (She'd) been living here for 10 years when I met her.