1.Adj：作定语,修饰名词,放在名词的前面eg.She is a beautiful girl.中的beautiful为形容词.
作表语,形容主语的某种特征eg.She is stupid.词句中stupid（愚蠢的）为形容词.
作状语,表示出于某种状态eg.United,we stand;divided,we fall!团结是我们巍然屹立,分裂是我们轰然倒下.此句中united团结的,divided分裂的极为形容词.
2.ADV：副词.作状语.副词种类很多.
1.可以用在形容词前面修饰形容词.eg.very stupid非常蠢.
2.还有一类连接性副词,eg.however,therefore.
3.还有一类有形容词变来的副词：即adj+ly形式,如beautifully,actually.
4.还有的词本身即可为adj也可为adv,如late,long.
3.N名词.一般在句中作主语.
他们是某些物体的名称.eg.desk桌子
一般放在限定成分的后面,如adj后,冠词（a,an,the）后面,数词（one,two,）后面eg.beautiful girl.the pig.three people.中的girl,pig,people就为名词.
4.V动词：在句中作谓语成分.She eats a big pig.此句中eat为动词,表示主语进行的某一个动作.
另外.动词还用于一下清醒：V-ing,to do sth,V-ed形式.分别举例：Eating a pig is difficult.句中eat,is 均为动词.It is difficult to eat a pig.（同上）A pig is killed and eaten.此句中三个动词：is.eat.kill.