This word are mainly using in the taking,and i rarely see this word in the writing.
わけshow the reason of something, so the image of this word in english is like "this is the reason why", "because", and "mean"
the reason why s/he can speak Japanese is (because) s/he studied it for three years.
Also you can make a negative sentence
it does not mean that if you study very harder right now, you can improve your grade immediately.