How long, when, for, since
FOR / SINCE: we want to say how long something has been happening.
FOR + periode of a time (one hour, one week, one year, etc …)
I’ve been working in this company for two years.
SINCE + start of the period (10 o’clock, Monday, 2005, 19th century, etc …).
I’ve been working here since June.
HOW LONG, WHEN:
HOW LONG + Present Perfect:
How long have they known each other?
They‘ve known each other for 10 years.
They‘ve known each other since last month.
How long have they been married?
They‘ve been married for 10 years.
They‘ve been married since 2005.
WHEN + Preterit:
When did you meet him?
I met him 10 years ago.
I met him when I was a student.
TIME EXPRESSIONS: