conjunction
Connects one event to what happened next. Common in speech and informal-to-neutral writing.
See also: そしたら
ボタンを押した。そうしたら、ドアが開いた。
I pressed the button. Then the door opened.
conjunction
Used after hearing or assuming some condition, to introduce what follows from it. Often conversational.
See also: そしたら
明日は雨らしい。そうしたら、家で映画を見よう。
It seems it will rain tomorrow. In that case, let's watch a movie at home.