Do has been called a helping verb; but it needs little observation to discover that it is no more so than a hundred other words.
With the helping verb ought, the difference in time is expressed in the infinitive.
With may and might and can and could, present and past time are expressed by a change in the form of the helping verb.
The difference in time is expressed by a change in the infinitive instead of a change in the form of the helping verb.
In interrogative sentences, the subject comes after the helping verb or after the interrogative used to introduce the sentence.
an informal term for an auxiliary verb, which combines with a main verb to help it express tense, mood, and voice
Common helping verbs are be, do, have, can, may, will, shall.