Auxiliary Verbs (from the Latin auxilio = to help; they are also known as helping verbs) are verbs‏‎ used to change the tense, form‏‎ mood and voice of other verbs.

In other words, we add an auxiliary to a verb to turn it into a question, to put it into the past, to make it negative and so on.
The 3 English Auxiliaries Verbs
There are three auxiliary verbs: be…