an interjection used to agree with someone or to express an impression — 'that's so', 'that's right', 'it seems so'.
A: 来週は忙しいよ。B: そうだね、予定を調整しよう。
A: I'm busy next week. B: That's true — let's adjust our plans.
そうだ、その方法ならうまくいくかもしれない。
That's right — that method might work well.
彼女、最近元気がないね。そうだね、様子を見に行こう。
She hasn't seemed herself lately. You're right — let's go check on her.
a hearsay expression meaning 'it is said that' or 'I hear that'; attaches after the plain form of verbs and adjectives.
明日は雨が降るそうだ。
I hear it will rain tomorrow.
彼は転職したそうだ。
I heard he changed jobs.
この店のケーキはおいしいそうだよ。
I've heard the cakes at this shop are delicious.