to do不定式用法总结如下：
1. 不定式的用法：
(1)作主语。不定式短语作主语时，为了使句子结构平衡，常将不定式短语放在谓语之后，而用it作形式主语。
It is our duty to give as much help as possible. 提供尽可能多的帮助是我们的职责。
但不定式作表语时，前面有不定式作主语，不定式不可位于句末。
To see is to believe. 眼见为实。
(2)作宾语。常见的只跟不定式作宾语的动词(组)有want, wish, hope, expect, would like (love),care, choose, learn, plan, prepare, mean, agree, promise, offer, refuse, ask, beg, decide, make up one’s mind, be determined, manage, try, can’t afford, fail, pretend等。
①He promised to come today, but he hasn’t turned up yet .
他许诺说今天来，但他到现在还没有出现。
②No one likes to be laughed at. 没人喜欢被嘲笑。
有形容词、分词、名词作宾补，不定式作宾语时要将不定式放于句末，用it 来作形式宾语。如：
You may find it necessary to finish the work ahead of time.
你会发现有必要提前完成工作。
(3)作宾语补足语。常见的跟不定式作宾补的动词有ask, order, advise, like, want, teach, force, forbid, beg, allow, expect, cause, invite, tell, know, call on, depend on, wait for等。
The children asked their parents to take them to the park.。
孩子们要求父母带他们去公园。
感官动词后，如 see, watch, look at, observe, notice, hear, listen to, feel及部分表示“使”、“让”的使役动词，如have, make, let 跟不定式作宾补时要省略不定式符号to。但在被动语态中to 要加上。
Though he had often made his sister cry, today he was made to cry by his sister.
尽管他总是弄哭他妹妹，今天却被妹妹弄哭了。
help后的不定式作宾补(包括作宾语)to 可有可无。