You use certainly to emphasize what you are saying when you are making a statement.
The public is certainly getting tired of hearing about it.
公众无疑厌倦了听这方面的事。
The bombs are almost certainly part of a much bigger conspiracy.
几乎可以确定这些炸弹是一个更大阴谋的一部分。
Today's inflation figure is certainly too high.
目前的通货数据的确太高了。
Certainly, pets can help children develop friendship skills.
宠物的确可以帮助儿童发展建立友谊的能力。
You use certainly when you are agreeing with what someone has said.
'In any case you remained friends.'—'Certainly.'
“不管怎样,你们还是朋友。” “那当然。”
You say certainly not to say 'no' in a strong way.
'Perhaps it would be better if I withdrew altogether.'—'Certainly not!'
“我完全退出的话情况或许会好些。” “当然不是。”