For and Since
We use ‚for‘ when we give a time period.
It is often used in present perfect a past tense.
I worked at M&S for 3 years. (not there any more)
I have worked in a bank for 2 years. (still working there)
Q: How long have you lived there? A: I’ve lived there for 12 years.
We use ‚since‘ when we say when some action has started.
After ‚since‘ goes some concrete point in time.
We usually use ‚since‘ with present prefect tenses but it’s possible to use with the past simple (depending on circumstances)
I have been a teacher since January 2010.
She has been married since summer last year.
He has wanted to be a fighter pilot since he was a little boy.