Form of the Present Perfect
The present perfect simple is formed with the auxiliary verb have in the corresponding form for the subject of the sentence, followed by the participle of the main verb.
Example sentences: I have finished my homework.
He has been in USA since 1999.
Present perfect is used for many different functions:
1-Actions which started in the past and are still continuing
Example: I have lived in London for twenty years. (I still live in London).
2-Actions which happened at a time in the past
Example: I have already visited Spain.
3-Actions which happened in the past, but have an effect in the present
Example: They‘ve been painting the flat.