帮我解释下动词不定式的用法.

动词 不定式
afford aim appear agree arrange ask be decide bother care choose come dare demand desire determine expect elect endeavor hope fail happen help hesitate learn long mean manage offer ought plan prepare pretend promise refuse seem tend wait wish undertake
动词不定式的基本形式是“to＋动词原形”,有时可以不带to.动词不定式（或不定式短语）没有人称和数的变化,在句子中不能作谓语.动词不定式仍保留动词的特点,即可以有自己的宾语和状语.动词不定式同它的宾语或状语构成不定式短语.
动词不定式具有名词、形容词和副词的特征,因此在句子中可以作主语、宾语、表语、宾语补足语、定语和状语.
1．作主语
作主语用的动词不定式常常用it替代,动词不定式（或短语）放在后面.例如：
It's easy to get lost in a big city like Tokyo．在东京这样的大城市容易迷路.
It is terrible to see the ship sinking into the sea．目睹轮船沉入大海,真是太可怕了.
2．作宾语
Indians like to eat hot food．印度人喜欢吃辣味食品.
They need to look at a map．他们需要查看地图.
有的动词不定式在作带有补足语的宾语时,前面往往带有形式宾语it.例如：
Do you think it necessary for us to learn to wait?你认为学会等待对我们来说很必要吗?
They improved the software to make it easier for people to use computers．他们改进了软件,使人们使用计算机更简便了.
3．作表语
It seems to be an interesting book．它看起来是本有趣的书.
The old man's job is to take care of the flowers in the garden．这位老人的工作是照料花园里的花.
4．作宾语补足语
He told me not to bring you anything．他叫我不要给你带任何东西.
Who taught you to play the music?谁教你弹这支曲子的?
5．作定语
动词不定式作定语时,要放在它所修饰的名词或代词后面.例如：
In my dreams I always have very difficult jobs to do．我在梦里总是做一些艰难的工作.
Every day he made one of the smaller animals bring him something to eat．他每天叫一个小动物给他带来吃的东西.
6．作状语
（1）表示目的
You can hide under my seat when the conductor comes to check the tickets．当列车员来查票时,你可以藏在我的座位下面.
In his third year,he left Harvard to work for a company called Microsoft．在三年级时,他为了去微软公司工作而离开了哈佛大学.
（2）表示结果
动词不定式作状语表示结果时常与副词too或enough连用.例如：
It's too heavy to carry．太重了搬不动.
The Californian ship arrived too late to save more people．加利福尼亚号来得太晚,没能挽救更多的人.
7．和某些形容词连用
和动词不定式经常连用的形容词有sure,ready,happy,sorry,afraid等.例如：
He's very happy to see his wife．他见到妻子非常高兴.
I'm sorry to trouble you．很抱歉打扰你了.
8．和疑问词who,what,when,where,which,how构成不定式短语作宾语.例如：
I don't know how to use a computer．我不知道怎样使用计算机.
Can you tell me when to start?你能告诉我什么时候出发吗?