Quote Originally Posted by Antonio1986 View Post
Спасибо для ваших ответов
Now I see what did you mean with "за" = "for".

This meaning of "за" is "in exchange for". (Я купил танк за три рубля.)

Here the difference "за" vs "для" is in the direction of casual connection.

"X для Y (Gen)" = first X then will be Y. Y is either an activity or someone who is able to use X (in some future activity).
"X за Y (Acc)" = first was Y then X. Y was an activity or a good and X is a pay-off in exchange for Y (compare to another meaning of "за" - "behind, after").