1.用法：常表示经常性、习惯性的动作；
e.g.Collecting information is very important to businessman.
Learning a foreign language is very useful to me.
Seeing is believing.
2.主谓一致：一个动名词（doing）作主语看作单数，两个动名词由and连接作主语看作复数；
e.g. Eating healthy food is important for us.
Playing and studying are two different parts of our daily life.
3.形式主语it：用it作形式主语，而把真正的主语(动词-ing形式)放在句末。常见句型有：
(1) It is/was no good/use/useless doing sth.干……没有好处/用处。
(2) It is/was a waste of time/money doing sth.做某事是浪费时间/金钱。
(3) It is/was worthwhile doing sth.做……是值得的。
e.g. It is no good waiting for other people to make decisions for you.
It is no use crying over spilt milk.覆水难收。
It is a waste of time talking about such useless things.
4.在there is no 结构中，通常用动词ing形式。常见句型有：
(1) There is no point/sense (in) doing sth.干……没有意义/道理。
(2) There is no pleasure doing sth.干……没有乐趣。
e.g. There is no point in persuading him any longer. He won't change his mind.
5.专题练习:
(1) _______(walk) is a good form of exercise for both men and women.
(2) —What made Jane so upset?
—________ (lose) the ring her husband bought her for her birthday.
(3) __________(find) a job in such a big company has always been beyond his wildest dream.
(4) _____________ (understand) your own needs and styles of communication is as important as learning to convey your affection and emotions.
(5) __________(know) basic first aid techniques will help you respond quickly to emergencies.
(6) It's no use_________ (speak) without taking action.
5.动词-ing形式的变化过则：
(1)一般情况下，直接加-ing;
e.g. go—going
ask —asking
look—looking
carry—carrying
(2)以不发音的e结尾的动词，去e加-ing;
e.g. write—writing
make—making
take—taking
move—moving
live—living
leave—leaving
(3)以重读闭音节（一个元音加一个辅音）结尾的动词，末尾只有一个辅音字母，双写这个辅音字母，再加-ing；
e.g. get—getting
sit—sitting
put—putting
run—running
begin—beginning
plan—planning
cut—cutting
get—getting
beg—begging
(4)注意（特殊）：
die—dying
lie—lying
tie—tying
picnic—picnicking
panic—panicking
listen—listening
develop—developing
答案见于公众号初高中英语学习资料