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" 日本語を三年もやったから、話せるわけだ。 the reason why s/he can speak Japanese is (because) s/he studied it for three years. Also you can make a negative sentence 今、一生懸命勉強したからと言って、成績がすぐに良くなるわけではない it does not mean that if you study very harder right now, you can improve your grade immediately.