You say of course to suggest that something is normal, obvious, or well-known, and should therefore not surprise the person you are talking to.
Of course there were lots of other interesting things at the exhibition.
展会上当然还有其他很多有趣的东西。
'I have read about you in the newspapers of course,' Charlie said.
“我当然在报纸上读过关于你的报道,”查理说。
You use of course in order to emphasize a statement that you are making, especially when you are agreeing or disagreeing with someone.
'I suppose you're right.'—'Of course I'm right!'
“我想你是对的。” “当然我是对的。”
Of course I'm not afraid!
我当然不怕!
You use of course as a polite way of giving permission.
'Can I just say something about the game on Saturday?'—'Yes, of course you can.'
“我可以就说说星期六的那场比赛吗?” “可以,当然可以。”
Of course not is an emphatic way of saying no.
'You're not really seriously considering this thing, are you?'—'No, of course not.'
“你并没有认真地考虑这件事,对吧?” “没有,当然没有。”