1.need+n.的时候,意思和want接近：
e.g.He needs money.
It doesn't need explanation.
2.need+to do是指需要做某事,主语是动作的发出者：
e.g.He needs to clean the house.
He doesn't need to clean the house.
3.need+doing也是指需要做某事,不过主语是动作的承受着,含有被动意：
e.g.The clothes need washing.（这个形式的否定很少见）
4.此外need还可用作情态动词,用在含有must do的问句的否定回答中.
e.g.-Must I do all the exercises?
-No,you needn't.(没必要)