The present perfect tense is a little bit tricky for non-native speakers of English. What I mean by tricky is that the action itself is in the past, but still relevant or has connection with the present. When you say I’ve lost the wallet that means you LOST the wallte in the PAST, but you have not got it NOW (the present). When you say I’ve just written a letter, the action of writing itself is finished when you say it. But the result of the action is in the present: the completed letter is on the table; you can see it NOW. In the two examples, we can also see that the definite time of the action is not mentioned because it is not important WHEN it happened or was completed.
Remember that the present perfect tense is used with have/has. Have is used with the pronouns I, You, and They. Have is also used with a plural subject, i.e. the boys, girls, women, etc.
So, the present perfect tense is used to talk about:
1. things that happened in the past, are finished when you say it, and have connection with the present (results or consequences of the action).
a. Pardi has gone to Jakarta (Pardi went to Jakarta sometime ago; he is not here NOW ).
b. I have posted the letter (I posted the letter sometime ago; the letter is not here NOW ).
C. The students have finished their homework (the students finished it sometime ago; you can see the completed work NOW).
2. things that happened at an unspecified time in the past. There is no mention of s pecific time because it is not important. WHEN it happened is not important. What is important to the speaker is they have already happened.
a. Budi: There’s a good movie on XXI. I want to see it. Do you want to come?
Pardi: Sorry I can’t. I HAVE SEEN it.
I HAVE SEEN it –> That’s why I don’t want to see it again. I saw it sometime ago, but it is not important WHEN.
b. Budi: What if we do the homework together? At your place, may be?
Pardi: Well, I HAVE already DONE it.
I HAVE DONE it –> I did/completed it sometime ago, but it is not important WHEN.
3. things that happened several times before now (in the past); the exact time is not important.
a. I have watched the movie three times now.
b. She has visited this place several times.
4. With some verbs, the present perfect tense is also used to talk about things that started to happen in the past, and are still hapennning right now. For this use, this tense is usually used with verbs such as teach, work, live, know. For or since is usually used.
THE PRESENT PERFECT TENSE VS THE SIMPLE PAST TENSE
Sometimes, many of us confuse the present perfect tense with the simple past tense.
a. Pardi has gone to Jakarta –> He went to Jakarta sometime ago (it is not important WHEN), and he is not here now; he has not returned.
Pardi went to Jakarta last week –> Pardi went to Jakarta a week ago (the definite time is mentioned), and perhaps he is/he is not here now (it doesn’t matter).
b. Pardi has written a letter –> He wrote it sometime ago (it is not important WHEN), and the letter is still on there on the table.
Pardi wrote a letter last week –> He wrote it a week ago (the definite time is mentioned), and it doesn’t matter whether the letter is still there on the table or not.
So, if there is no mention of the exact time, use the present perfect tense. If the specific time is mentioned, use the simple past tense.