Present Perfect is formed by means of the auxiliary verb have (has for 3rd person singular) in Present Tense and Past Participle (3rd form of irregular verbs or -ed ending for regular verbs).
For example:
I have lived in Russia for 2 years. (I’ve)
He has lived in Russia for 2 years. (He’s)
They have lived in Russia for 2 years. (They’ve)
I have not lived in Russia for 2 years. (I’ve not)
He has not lived in Russia for 2 years. (He’s not)
They have not lived in Russia for 2 years. (They’ve not)
Have I lived in Russia for 2 years?
Has he lived in Russia for 2 years?
Have they lived in Russia for 2 years?
Cases of using:
1. Recently completed actions
She has tidied her room. (She has finished tidying her room. You can see it is tidy now. — evidence in the present)
2. Actions which happened at an unstated past time and are connected with the present
He has lost his keys. (He is still looking for them.)
3. Personal experiences/ changes which have happened
I’ve lost 10 kilos.
4. Emphasis on number
She’s written three letters since this morning. She has called on two clients since 12 o’clock.
Time expressions used with:
just, yet, never, already, ever, so far, up to now, recently, since, for, yet etc.