Question

when we have to use since &for

Answer 1

with perfect continuous tenses :)

Answer 2

To use since/ for

I have been study English since 2010 (Since - To specify the year, month, day, hour ...) I have been study English for 3 years ( For - To specify how long you are doing this)

I hope you understand

Answer 3

you can refer to the post below:

https://plus.google.com/b/103882111250177228305/103882111250177228305/posts/b4MsNbwi6zg