Do is a verb for actions, work, and activities. It often means to perform something. In English, do can also be an auxiliary verb, so the meaning depends on the sentence.

In the present tense, do changes with the subject. I, you, we, and they use do. He, she, and it use does.

Subject	Form
I	do
You	do
We	do
They	do
He	does
She	does
It	does

Do is common for general actions and activities. It often appears with broad activity words, not with one clear physical action. Many everyday combinations with do must be learned as phrases.

Word or Phrase	Definition
do homework	This means to complete school work.
do housework	This means to clean and manage work at home.
do exercise	This means to do physical activity for health.
do work	This means to perform a job or task.
do a job	This means to complete a piece of work.

Some expressions use do as a fixed part of the phrase. In these phrases, English uses do because that is the usual form. Different speakers may prefer different phrases in some situations.

Word or Phrase	Definition
do your best	This means to try as much as you can.
do business	This means to work in trade or money activity.
do harm	This means to cause damage or bad effects.
do good	This means to help people or create good results.
do time	This means to spend time in prison.

Do is used in short answers in basic conversation. It answers yes and no questions with do or does. The form in the answer matches the form in the question.

Rule
Use do in a short answer with I, you, we, or they.
Use does in a short answer with he, she, or it.
Use do not or does not in a negative short answer.

Do is also an auxiliary verb in simple present questions. It helps make questions with most main verbs. In this use, do does not show the main action by itself.

Rule
Use do before I, you, we, or they in a simple present question.
Use does before he, she, or it in a simple present question.
Use the base form of the main verb after do or does.

Do is also an auxiliary verb in simple present negatives. It helps make negative sentences with most main verbs. In this use, the main verb stays in the base form.

Rule
Use do not with I, you, we, or they in a simple present negative sentence.
Use does not with he, she, or it in a simple present negative sentence.
Use the base form of the main verb after do not or does not.

You can now use do for common actions and fixed phrases in simple English. You can choose do or does in present forms and short answers. You can also recognize do as a main verb or as an auxiliary in simple questions and negatives.