1. 动词的ing形式包括动名词和现在分词，二者都可作表语。如：
Our job is playing all kinds of music . ( 动名词 )
The music they are playing sounds so exciting . ( 现在分词 )
注：一般来讲，动名词 ( 短语 ) 作表语，主表可互换，即：Playing all kinds of music is our job.
现在分词作表语，表明主语的性质和特征，主表不可互换。
2. - ing形式做定语可以表示
1 ) 所修饰名词的用途
a waiting room ( = a room for waiting ) / a walking stick ( = a stick for walking )
2 ) 所修饰名词正在进行的动作，可以换成定语从句形式
a waiting man ( = a man who is waiting ) / a sleeping child ( = a child who is sleeping )
3. 在see , hear , feel , watch , notice等感观动词后可以用 - ing形式做宾语补足语。这时 - ing形式和句子的宾语之间存在着逻辑上的主谓关系，并且 - ing形式表示宾语正在进行的动作。如：
He saw a girl getting on the tractor. ( = He saw a girl and the girl was getting on the tractor . )
Do you hear someone knocking at the door?
1).做宾语补足语We watched three boys sharing their food with each other.
2).做主语补足语She was heard singing in the next room.
3).做表语和定语My job is teaching English. /a walking stick/a waiting room
当-ing分词做定语的时候，常常放在被修饰名词的后面
The girl singing now is a classmate of mine.
4).做伴随、原因、时间、结果状语
He sat at the desk reading a magazine.
Being very young, he can't dress himself.
Having finished all the work, they went to the shore.
Her parents died, leaving her a big house.
