‘I have been to Boston.’
Have/has + past participle makes the present perfect.
She has lost her bag.
They have taken a taxi
I have been to Australia
The present perfect tense is used to describe something that happened in the past, but the exact time it happened is not important. It has a relationship with the present.
I have done my homework = I finished my homework in the past. It is not important at what exact time, only that it is now done.
I have forgotten my bag. = Exactly when in the past that I forgot it is not important. The important thing is that I don’t have it now.
As we do not use exact time expressions with the past perfect, we cannot say:
I have done my homework
In this case we use the past simple tense:
I did my homework yesterday.
Using already just and yet with the present perfect
Already, just and yet can are all used with the present perfect.
Already means ‘something has happened sooner than we expected:
‘The movie only came out yesterday, but I have already seen it.’
Just means ‘a short time ago’:
‘I have just seen your brother going into the bank with a gun!’
Yet is only used in questions and negative sentences. It means ‘something is expected to happen’:
‘Have you finished the report yet?’
No, I haven’t finished it yet.’