Do-insertion or Do-support

In English grammar, ‘do-insertion’ or ‘do-support’ refers to the use of the auxiliary verb ‘do’, including its reflected forms ‘does’ and ‘did’. There are some common uses of do-insertion which are described below.

To ask a question:

We consider a sentence, “You want money”.
Here, ‘you’ is the subject, ‘want’ is the verb and ‘money’ is the complement. But there is no auxiliary verb in this sentence. That’s why we need to add a dummy ‘do’ to turn this assertive sentence into an interrogative sentence.

• You want money (You do want money).
  -Do you want money?

Similarly, 

• She likes the dress (She does like the dress).
  -Does she like the dress?
• He got the job (He did get the job).
  – Did he get the job?

To make a negative sentence:

We need to add the word ‘not’ to the auxiliary verb.
Example:

• You want money.
  -You do not want money/ You don’t want money.

Similarly, 

• She likes the dress.
  -She does not like the dress/ She doesn’t like the dress.
• He got the job.
  -He did not get the job/ He didn’t get the job.

Note: In most cases, we need to add the auxiliary ‘do’ to make a question or negative sentence except the use of the verb ‘be’ and the verb ‘have’.