Auxiliary (or Helping) verbs are used together with a main verb to show the verb’s tense or to form a negative or question. The most common auxiliary verbs are have, be, and do.
Does Sam write all his own reports?
The secretaries haven’t written all the letters yet.
Terry is writing an e-mail to a client at the moment.
Auxiliary verbs, also known as helping verbs, add functional or grammatical meaning to the clauses in which they appear. They perform their functions in several different ways:
By expressing tense ( providing a time reference, i.e. past, present, or future)
Grammatical aspect (expresses how verb relates to the flow of time)
Modality (quantifies verbs)
Voice (describes the relationship between the action expressed by the verb and the participants identified by the verb’s subject, object, etc.)
Adds emphasis to a sentence