1.Auxiliary verbs (sometimes known as helping verbs) are verbs that are used to assist the verb.
2.Auxiliary verbs can not be used without a main verb.
3.Auxiliary verbs can not be used with modal verbs.
4.Auxiliary verbs are used to make sentences negative.
5.Auxiliary verbs are used to ask questions.
6.Auxiliary verbs are used in the sentence structure of the verb sentence.

The 3 most common auxiliary verbs are:

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Do – Does – Did
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Do is used with the present simple tense. Do-Does are used as part of the sentence structure for negative statements/sentences with the present simple tense
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Do- Does are used as part of the sentence structure for questions, with the present simple tense.
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Did is used with the past simple tense.
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Did is used as part of the sentence structure for negative statements/sentences with the past simple tense
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Did is used as part of the sentence structure for questions, with the past simple tense.
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Be – Am – Is – Are -Was – Were
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Have – Has -Had

DO’, ‘BE’ and ‘HAVE’ are the English auxiliary verbs used in a negative structure, a question or to show tense.

DESCRIPTIONS OF ENGLISH AUXILIARY VERBS:

1. ‘DO’, ‘DON’T', ‘DOES’ and ‘DOESN’T’ are used for questions and negatives in the Present Simple Tense, and ‘DID’ and ‘DIDN’T’ are used in the Past Simple Tense.

2. ‘BE’ is used with the Present Participle in Continuous (Progressive) Verbs. It is also used with the Past Participle in the Passive.

3. ‘HAVE’ is used with the Past Participle to form the Perfect Aspect.

Source www.english-the-easy-way.com