The main verb and helping verb (also called auxiliary verb) are essential components of a sentence.

The main verb expresses an action and conveys the core meaning of that action, e.g., eat, write, buy, wash. These verbs provide the principal information about the nature of an action. For instance, the verb eat means the act of chewing and swallowing food.

In contrast, a helping verb does not give the basic meaning of an action on its own, but it is used with a main verb in a sentence to indicate the time of the action. The helping vebrs (or auxiliary verb) specifies when an action occurs—whether in the past, present, or future—rather than the action itself.

Examples of auxiliary verbs: is, are, was, were, has, had, will, etc.

Thus, the main verb provides the fundamental meaning of an action, while the auxiliary verb expresses the time of the action—such as when the action occurred, occurs, or will occur.

Examples:

Example.

• He is sleeping.     (action in the present)
• He was sleeping.  (action in the past)

In the first example, the auxiliary verb ‘is’ indicates that the action (sleeping) is occurring in the present. In the second example, the auxiliary verb ‘was’ shows that the action took place in the past. Auxiliary verbs are therefore used according to the tense of the sentence to convey temporal context.

Since the main verb conveys the core meaning of action, it is also referred to as the principal verb. Similarly, the auxiliary verb, which helps the main verb in completing the meaning of a sentence, is also called a helping verb.

There are two types of auxiliary verbs: 1) Primary Auxiliaries, and 2) Modal Auxiliary.

   Types of Helping Verbs (Auxiliary Verbs)

Auxiliary verbs are categorized into two types:

1. Primary Auxiliaries
2. Modal Auxiliaries

There are three primary auxiliary verbs: be, do & have. Their usage depends on the tense of the sentence.

  Be: The auxiliary ‘be’ has present forms (is, am, are) and past forms (was, were). They are used in the continuous tenses.

Examples.

• I am drinking water. (Present continuous tense)
• He is writing a letter. (Present continuous tense).
• They are going to school. (Present continuous tense).
• He was waiting for a bus. (Past continuous tense).
• They were playing football. (Past continuous tense).

  Have: The auxiliary ‘have’ has present forms (have, has) and past form (had). They are used in perfect tenses.

• He has passed the exam. (Present perfect tense).
• I have bought a cameral. (Present perfect tense).
• She had finished her work. (Past perfect tense).
• I had received the letter. (Past perfect tense).

  Do: The auxiliary verb ‘do’ has present forms (do, does) and past form (did). They are used in question and negative sentences in present and past simple tenses.

• I do not eat vegetables.   (Present simple tense).
• He does not go to school. (Present simple tense).
• I did not win the prize.   (Past simple tense).     
• She did not break the cup. (Past simple tense).

Note. The auxiliary ‘be’ has also the form ‘been’ which is used along with a form of "have" (e.g., has, have, had) in perfect continuous tenses.
Examples.

• He has been working in a factory since 2018.    (Present perfect continuous tense).
• They have been watching a movie since morning. (Present perfect continuous tense).
• He had been teaching students for three years. (Past perfect continuous tense).
• They had been running a business since 2015. (Past perfect continuous tense).

Modal auxiliaries are used to show ideas like possibility, ability, necessity, or intention.

Examples.
Could, Can, (ability)
Might, May  (possibility)
shall, will would (intention)
Should (necessity)
Ought to (necessity)
Must (necessity)

Modal auxiliaries are placed before the main verb as helping verbs in a sentence.

Examples
He can drive a bike.
He may come now.
A student must take his exams.
They might come today.
He must reach in time.