"そうか"　"そうですか"　"なるほど"　"わかります"?
What is the difference in the usage of these expression? If you could give examples sentences or situations, that would be awesome. Thanks! :)

Question

Answer

そうですか is the polite form for "Oh, really?" (usually rhetorically when listening to someone)
そうか or そっか are informal forms of そうですか
なるほど is more like "I see"; like someone explained something to you