1.形式宾语：
find/think/make + it+ adj. + to do sth/that 从句(宾语从句)
I find it interesting to learn English.
2. 形式主语：
1) It + be + adj. + (for/of sb.) + to do sth.
It is kind of you to help me when I am introuble.
It is important for you to learn English in youruniversity.
2) It takes/took sb. + 一段时间 + to do sth.
It takes me ten minutes to finish the task.