Basic usage:

1) means that the action took place in an uncertain time in the past, but it has left some influence and results on the present. It is often modified by adverbs such as just, always and yet.

2) indicates the action or state from a certain moment in the past to the present. This action may have just stopped, or it may continue. There are often adverbials, such as for, since, in the past, in the past ..., the whole week, so far, and so on. Indicates a period of time.

3) It means that one or more actions have taken place before speaking, and now it has become an experience. Generally speaking, it is translated into Chinese "Guo", often with adverbials of time, such as twice, once, never and three times.

Affirmative sentence: subject+auxiliary verb have/ you+past participle+others

Explanation: have/has here is an auxiliary verb and has no specific meaning. When the subject in the third person is singular, the auxiliary verb uses has, and the others use have. The abbreviations of has and has are' s or' ve, respectively.

For example:

I have just copied all the new words. I just copied all the new words. (means don't copy again)

She lost her book .. She lost her book. (indicating that it has not been found so far)

We have just cleaned the classroom. We have just cleaned the classroom. (indicating that the classroom is clean now)

Negative sentence: subject+auxiliary verb have/has+not+ past participle+others

Explanation: When the present perfect tense constitutes a negative sentence, just add not after the auxiliary verb have/has. The abbreviations of have not and have not are haven't and hasn't, respectively. In addition, when some and are already in affirmative sentences, they should be changed to any and yet when they are changed to negative sentences.

For example:

1) I haven't finished my homework.

2) He has never been on a train .. He has never traveled by train.

We have never talked to foreigners.

Note: sometimes not can be replaced by never, which means "never"

Another example is:

I have never seen him before. I have never seen him before.

General question type: auxiliary verb Have/Has ++ subject+past participle+others?

Explanation: Put have or has at the beginning of a declarative sentence, put a question mark at the end of the sentence, and change some and always in the sentence to any and yet to form a general question. The affirmative answer is "Yes, subject++Yes/Yes ..." The negative answer is "No, subject +have t/ Not yet". Sometimes you can also use "No, not yet. /No, not once ... "。

For example:

1)— Have you ever packed jiaozi? Have you ever been a jiaozi?

Yes, I do. Yes, I do.

2) Has he been abroad? Has he ever been abroad?

No, never. No, never.

Did they find the lost money? Did they find the lost money?

Yes, they did. Yes, they found it.

Note: when there are negative words not, hardy (almost) and never in the sentence, when it is changed into a question, the additional part is in a positive form.

For example, you have never been to our school, have you?

You have never been to our school before, have you?