你说的是动名词doing做主语,这个时候相当于把动词名词化,当名词来用
比如：
Doing my homework is important. Doing my homework就是主语,谓语是is
也可以用to do形式表达
To do my homework is important.
To have my homework done is important.
Having my homework done is important.
to do, done 和doing 都可以做非谓语成分（有时候是定语或状语,不一定都是做主语）
区别是,to do 有将要的意思,也可表目的,doing有正在进行的意思,done强调做过或者是被动
doing 和 to do 很多时候区别不大 你说的是动名词doing做主语,这个时候相当于把动词名词化,当名词来用
比如：
Doing my homework is important. Doing my homework就是主语,谓语是is
也可以用to do形式表达
To do my homework is important.
To have my homework done is important.
Having my homework done is important.
to do, done 和doing 都可以做非谓语成分（有时候是定语或状语,不一定都是做主语）
区别是,to do 有将要的意思,也可表目的,doing有正在进行的意思,done强调做过或者是被动
doing 和 to do 很多时候区别不大