1. Unit 2 Grammar
Present Perfect Tense can be used in three situations: 1. To indicate something that has happened at an indefinite time in the past. I have seen that movie already. She has left for California. They have not eaten their dinner yet.

2. Unit 2 Grammar
2. To indicate something which started in the past and continues until now. I have lived in New York for nine years. We have been here since Friday. He has played football since he was a child.

3. Unit 2 Grammar
3. To indicate something which occurred recently. I have been sick lately. She hasn't slept much recently.

4. Grammar 2 Present Perfect Notes
When speaking about a specific time, use past tense.
A: I have seen that movie already.
(Non-specific time)
B: Oh really? When did you see it?
A: I saw it last week with Bob.
(Specific time)

5. Unit 2 Grammar Some words should not be used in situation 2 (above)
I have met John for five years.
(INCORRECT)
I have known John for five years.
(CORRECT)
I met John five years ago.
I have met John already.

6. Unit 2 Grammar Notes
Sometimes, but not always, present perfect continuous can be used instead of present perfect.
I have lived there for ten years
(Okay)
I have been living there for ten years.
I have exercised a lot recently.
I have seen that movie ten times.
I have been seeing that movie ten times.
(NOT Okay)