1.主语：是句子要说明的人或事物,是句子的主体,一般由名词、代词、数词、不定式或动名词等充当.如：
The car is running fast.(名词)
We are students.(代词)
One of my classmates is from Shanghai.(数词)
It's bad manners to spit in public.(不定式)
Eating too much is bad for your health.(动名词)
【注意】若不定式短语作主语常用it作形式主语,而把真正的主语(不定式短语)放在句后.
2.谓语：说明主语的动作或状态,也是句子的主体部分,一般由动词充当.动词分为实义动词、连系动词、情态动词和助动词.实义动词单独作谓语,连系动词与表语一起构成谓语,情态动词与省略to的不定式构成合成谓语,助动词与动词原形共同构成谓语部分.如：
He works in a factory.(实义动词)
I felt cold.(系动词＋表语)
How can I get to the station?(情态动词＋实义动词)
Do you speak English?(助动词＋实义动词)
They are working in a field.(助动词＋实义动词)
【注意】谓语与主语在人称与数方面要相互照应.
3.宾语：是及物动词所涉及的对象,一般由名词、代词、不定式及动名词等充当.如：
He is doing his homework.(名词)
They did nothing this morning.(代词)
She wants to go home.(不定式)
We enjoy playing football.(动名词)
http://edu.sina.com.cn/zhongkao/2008-02-12/1332122048.shtml
详细的解释,这个网上有,解释得非常清楚,希望可以帮到你