HOW TO FORM IT: Since and for both introduce periods of time. Since refers to the time period when something began. For is used to express the duration, or length, of the activity.
We have been living in San Francisco for ten years.
We have been living in San Francisco since 1996.
I’ll be in Paris for a week.
I’ve been in London since last Tuesday, and I’m leaving tomorrow.
Expressions and idioms with since & for:
Joan has been studying Chinese for ages and she still doesn’t speak it well!
(for ages = for a very long time!)
We’ll be staying in this apartment for the time being.
(for the time being = for now; for a while)
Since when do you wear cologne to school?
(since when = when did you start doing that?)
Ever since you told me that Cindy likes to gossip, I haven’t told her anything.
(ever since = starting when; since the time when)