For
For a period of time
I haven’t been skiing for four years
I have been working down the mines for 35 years.
Since
From a point of time until now.
I haven’t skied since I was seven years old.
I have been working down the mines since I was a young child.
For and since questions
1) How long is it since you went to school?
2) How long have you been working ?
3) When did you pass your driving test?
4) When did you first realise you wanted to work in a laboratory testing animals food?
5) How long is it since Barcelona FC won the league?
6) How long have the lorry drivers been on strike for?
Example: I have been working as in English teacher in the north of Spain since 2019.