Question

i am of the opinion that 怎么用

Answer 1

of the opinion that +同位语从句（表示opinion 的具体内容）
认为…,相信…;主张
I am of the opinion that we should do it at once
我认为我们得马上做这件事

Bill is of the opinion that the results of professional wrestling matches are fixed.
比尔相信，职业摔跤角比赛的结果是预先安排的。

Answer 2

很容易：
I am of the opinion that ... = I think (that) ...
(别在口语中用 I am of the opinion that ...，否则英语为母语的人认为你 speak like a book 。)