PRESENT PERFECT:
The present perfect is formed with the helping verb "Have" in the present form (have or has) plus the past participle of a verb: For example: He has studied English.
If the verb is irregular, the past participle is the third form (write, wrote, WRITTEN). For example: We have sung that song.
Remember the spelling rules:
a) if the verb is regular, then you have to add "-ed" to the base form: work --> worked.
b) If a verb ends in "-e" you only add "-d": love --> loved; Like --> liked.
c) If the verb ends in consonant + y, you need to change "y" by "i": Hurry--> hurried; Study --> studied
d) If the verb has only one syllable and ends in consonant + vowel + consonant, the final consonant is doubled: stop --> stopped.
e) If the verb ends in a single consonant after one short and stressed vowel, this final consonant must be doubled: admit --> admitted; Prefer --> preferred
f) If the verb ends in "l" after one short vowel, it must be doubled: Travel --> travelled.
You should take care with "been" and "gone" as the past participles of the verb "to go": If you have visited Japan on holiday and then returned home, you should say: "I have been to Japan".
On the contrary, If you visit Japan but you have not come home yet, you should say: "I have gone to Japan".