grammar word summary: Since can be: ■ a preposition: Everything has changed so much since last spring. ■ an adverb: She left home in 1993 and hasn't been seen since. ■ a conjunction: Paul's had several different jobs since he left school.
1) from a particular point in the past until now, or until another point in the past
I've known Joanna since she was born.[/ex]
Turkey has been a republic since 1923.[/ex]
I'd not seen her since she went to live in Oxford.[/ex]
Since arriving in New York, Thomas has had 15 job interviews.[/ex]
Paul started sailing in 1986 and he's been doing it ever since.[/ex]
2) used when giving a reason
Since Barbara is no longer my wife, I'm not responsible for her debts.[/ex]
since when?spoken used for showing that you are surprised or annoyed by something[/ex]
Since when has it been against the rules to have a coffee break?[/ex]
Both since and for are used for saying how long something has been happening. ■ Use since to introduce a particular time or event when something started: I've been working here since 1980. ■ Use for to introduce the period of time during which something has continued: They've been married for over 40 years.

Dictionary for writing and speaking English. 2014.