★For and since

We use for and since to say how long something has been happening.

☆★☆
For + a period of time ( two hours, six weeks, etc.):

☆I've been waiting for two hours.

       Two hours ago →now

Used when we measure the duration of something or how long it last.

for → two hours / 20 minutes /five days /a long time /six months /50 years /a week
ages /years

☆Sally has been working here for six months.(not since six months)

☆I haven't seen Tom for three days.
☆Paul has lived in Brazil for ten years.
☆I'm tired of waiting. We've been sitting here for an hour.
☆I haven't been to a party for ages.
☆The weather is dry. It hasn't rained for a few weeks.
☆We have been married for 10 years.
☆He has been playing for three hours.

☆★☆
It is possible to leave out for (but not usually in negative sentences):

☆They've been married (for) ten years. (With or without for)

☆They haven't had a holiday for ten years. (You must use *for )

☆★☆ 

We do not use for + all ... (all-day / all my life etc):

☆I've lived here all my life  (not for all my life)

☆★☆

You can use in instead of for in negative sentences (I haven't... etc.):

☆They haven't had a holiday in ten years (= for ten years)

☆★☆☆★☆

Since + the start of a period (8 o'clock, Monday, 1999 etc.):

from that point in time until the present

☆I've been waiting since 8 o'clock.

8 o'clock → now

since → 8 o'clock /Monday /12 May /April /2001 /Christmas /lunchtime /we arrived /

I got up

☆Sally has been working here since April (=from April until now)

☆I haven't seen Tom since Monday.
☆It's been raining since lunchtime.
☆Sarah has lived in Paris since 1995.

☆I wonder where Joe is. I haven't seen him since last week.
☆I have been working here since 2011.
☆Jana is away. She's been away since Friday.
☆Kevin has been looking for a job since he left school.