Do has three main uses.
Auxiliary verb
As an auxiliary verb do is used with other verbs to form emphatic, interrogative, negative and shortened verb forms.
- Does he smoke? (NOT Smoke he?)
- I do like this kind of music. (More emphatic than I like this kind of music.)
- She doesn’t work with us. (NOT She works not with us.)
- ‘My hair needs cutting.’ ‘Yes, it certainly does.’ (= Yes your hair needs cutting.)
As a general purpose verb
Do is also an ordinary verb. As an ordinary verb, do can refer to almost any kind of activity. It is used when it is not necessary to be more precise.
- What are you doing there?
- Why did you do that?
- I have washed the clothes; now I will do the dishes.
- All I did was to give him a little push.
Do as a substitute verb
In British English, do is used as a substitute for the main verb after an auxiliary. In American English, do is not normally used with this meaning.
- ‘Do you think she will accept our offer?’ ‘She might do’ (GB) ‘She might.’ (US)
Auxiliary do and non-auxiliary do can occur together.
- I don’t (auxiliary) do (non-auxiliary) much reading.
- How do you do?