conjunction
Casual conjunction linking a reason to a result. Often used at the start of a sentence in spoken Japanese. The polite equivalent is ですから.
See also: ですから
雨が降っている。だから、傘を持っていこう。
It's raining. So, let's take an umbrella.
彼はよく勉強した。だから、試験に合格した。
He studied hard. That's why he passed the exam.
expression
like I said; I told you so
Used at the beginning of a sentence to express irritation or to remind someone of a previous statement. Often carries a tone of 'See? I told you.'
だから言ったでしょ、早く出ないと遅れるって。
See, I told you we'd be late if we didn't leave early.
だから、あの店はやめておけって言ったのに。
I told you to stay away from that store.