1. Duration of time: For, since, and ago.

2. FOR
To express a specific duration of time, e.g.: one week, two years, an hour.
For + period: a "period" is a duration of time - five minutes, two weeks, six years. For means "from the beginning of the period to the end of the period".
Use the Present Perfect
He has been living on this island for two years.
He’s been waiting for a long time.
He hasn’t spoken to anyone for two years.
For can be used with all tenses. Here are a few examples:
1. They study for two hours every day.
2. They are studying for three hours today.
3. He has lived in Bangkok for a long time.
4. He has been living in Paris for three months.
5. I worked at that bank for five years.

3. SINCE
To indicate a time, an event, or specific moment which continues into the present.
since + point : a "point" is a precise moment in time - 9 o'clock, 1st January, Monday. Since means "from a point in the past until now".
Use the Present Perfect
I’ve been here since the shipwreck.
It’s been raining since yesterday.
Since is normally used with perfect tenses:
He has been here since 9am.
He has been working since he arrived.
I had lived in New York since my childhood.
We also use since in the structure "It is [period] since":
It was a year since I had seen her.
How long is it since you got married?
It has been two months since I last saw her.
It has been three years since the last earthquake.

4. DIFFERENCE BETWEEN “FOR”AND SINCE”
for a period from start to end
since a point from then to now
>===<
x===>|
for 20 minutes for three days for 6 months for 4 years for 2 centuries for a long time for ever
since 9am since Monday since January since since since I left school since the beginning of time
all tenses
perfect tenses

5. AGO
Indicates a time in the past; how much time since the action or event took place.
Use the past tense
I arrived on this island two years ago.
A helicopter saw me ten minutes ago.

6. Complete the phrases with (for, since, ago)
E.g.: I’ve been riding a bike _____ I was three.
I’ve been riding a bike since I was three.
1. She’s been living in Montreal _____ she moved to Canada.
2. I had been working_________  5 o'clock and I was getting tired.
.3. She has been writing thrillers _____ the 80s.
4. I work in New York _____ 7 years.
5. He has lived in Bangkok_________ a long time.
6. He has been living in Paris __________three months.
7. I worked at that bank ___________ five years.
1. Since 2. since 3. since 4. for 5. for 6. for 7. for

7. Complete the phrases with (for, since, ago)
8)I've been waiting ____________ 7 o'clock.
9)They exercise_________  two hours every day.
10) I have known him______ January.
11) She moved to Chicago six months ____
12) I have been here_____  5 o'clock and I am getting tired.
13) I have known her _________  a long time.
8. Since 9. for 10.  since 11. ago 12. since 13. for

8. Complete the phrases with (for, since,)
1. They have been living in Madrid_______ He has been in prison_______ four years. 3. He has known about the fact __________ a long time. 4. Conditions have changed a lot__________ we were children. 5. Our teacher has been very ill__________ the last month. 6.I haven't eaten anything___________ twenty-four hours.
1. since
2. for
3. for
4. since
5. since
6. for

9. Complete the phrases with (for, since,)
7. In fact he is always very rude. We have been waiting for him_________ half an hour.
8. I haven't seen him for three years. It is because I haven't been there_________ I left school.
9. I have been trying to mend this old fashioned car____________ hours.
10. One of my friends has been teaching in Tokyo three years. I haven't met him __________last year.
11. I haven't enjoyed myself two weeks _________I heard that my final exam grades were low.
12. I know that you have never seen a lion_____________ you were born. Then now I say that we can go to the zoo and see one.
7. for
8. since
9. for
10. for
11. for
12. since

10. Answer these questions…
1.How long have you been living in _____?
2. When did you finish your degree?
3. How long ago did you last see your best friend?
4. Since when have we been doing this lesson?