We usually use short forms (I've, You've, He's, She's, We've, They've) when we are speaking and in informal writing.
Regular verbs have past participles which are the same as their past simple forms, ending -ed.
- We visited London. → She's visited many cities.
- The letter arrived yesterday. → The letter has arrived!
Irregular verbs have irregular past participles. Sometimes the past participle of an irregular verb is the same as the past simple form.
- They had dance lessons last year. → We've had swimming lessons.
- We met for a coffee last week. → They've met many times before.
Sometimes the past participle of an irregular verb is different from the past simple form.
- She did some homework last night. → She's done lots of homework.
- I spoke to the manager yesterday. → I've spoken to the manager.