what is 해오다??
as in 숙제 해오세요.if it's equal to 하다 then what's the different in usage?

Question

Answer

하다 means 'to do' in English, and 숙제하다 means to do homework.
In addition, 아/어 오다 means 'come having done something,' so...

숙제하세요 means please do your homework.
숙제해 오세요 mean please come having done your homework
or do your homework before you come.

Similarly,

숙제했어요 means, I did my homework.
숙제해 왔어요 means, I have done my homework.