Do and does usage

The use of do/does depends on the subject of the sentence.

Do is used with subjects such as I we they etc and plural noun subjects. eg

I do my home work at night. They do their homework in the morning. - pronoun subjects

The girls do their homework at night -- plural subject (the girls).

Does is used with he, she, it and singular noun subjects. eg

She does her homework. It does the work of five men. -- pronoun subjects

The doctor does the accounts. -- singular noun subject (the doctor).

Usage is similar in questions:

Do you like ice cream?

Does she like ice cream?