One special category of verbs are helping verbs, also called "auxiliary verbs."
These verbs do not mean anything on their own.
They just "help" the main verbs to express their full meanings, and are necessary for grammatical structure of a sentence.

For example:

The school bus had broken down this morning! (had, a form of have, is the helping verb, broken is the main verb)
The students were walking to school when another bus picked them up. (were, a form of be, is the helping verb, picked is the main verb)
They should have just waited at the bus stop. (Both should and have are helping verbs, and waited is the main verb)

You can see that, on their own, these auxiliary verbs don't really mean anything - sentences like "The school bus had." or "The students were." or "They should have." don't mean anything on their own, but in the context of the sentence, they change the meaning of the other verbs, by making them past or future tense, by implying a suggestion, or in many other ways we will see later in the lesson.

Categories of Helping Verbs

All the helping verbs can be divided into 3 broad groups:

1. Primary Helping Verbs: be, do, have

These verbs change form to match the subject.

For example:

I have

She has

I do

She does

I am

She is

These verbs can be used as the main, or primary, verb in the sentence.

They are considered helping verbs if they function in these ways:

HELPING VERBS	FUNCTIONS	EXAMPLES
Be	forming progressive tenses	We are fishing.
	showing the passive voice	The book was written in 1850.
Have	forming perfect tenses	They have already eaten.
Do	asking questions	Did you take the bus?
	forming negatives	He does not study as much as he should.
	emphasizing something	We do care if you succeed.
	replacing a main verb if it was already referred to	I run slower than you do.

These verbs are considered auxiliary verbs, because they are only serving a grammatical function, not adding new information. This makes them different from modal verbs, which are the next category we will discuss.

2. Modal Verbs or Modal Auxiliaries or Modal Helping Verbs: can, could, may, might, will, would, shall, should, must, ought to

These are a very special type of verbs because they are always used in the same form - they don't change to match their subjects.
These modal verbs change the meaning of the main verb in some way, often by expressing advice, necessity, ability, expectation, or possibility.
The main verb that follows is always the "bare infinitive form" - the basic verb without "to" before it.

For example:

It can't rain on my birthday!
We should probably cancel it.
We may not be able to have a party!
Would you want to have a party in the rain?

3. Semi-Modal Verbs: need, dare, used to

These verbs function a lot like modal verbs because they add more information to the sentence, but must be used before another verb.
Unlike modal verbs, however, they sometimes change form (for example, need might change to needs, and dare can change to dared).
Because of this difference, we call these verbs semi-modal.

For example:

She dares to go sky diving. I don't dare to sky dive!
We used to have math homework every evening, but we didn't use to have reading.
I need to study every night, she needs to study every night, but they don't need to study at all!

Summary

A verb is a word that can express a physical action, a mental action, or a state of being.
- For example: She learns new things everyday.
Helping verbs are a special category of verbs.
They do not mean anything on their own. They just "help" the main verbs to express their full meanings, and are necessary for grammatical structure of a sentence.
All the helping verbs can be divided into 3 broad groups:

Primary Helping Verbs

[these verbs change form]

Modal Verbs or Modal Auxiliaries

[these verbs NEVER change form]

Semi-modal Verbs

[partly modal, partly main verb]

BE (am, is, are, was, were, being, been)

DO (does, do, did)

HAVE (has, have, had, having)

can, could,

may, might,

must,

shall, should,

will, would

ought to

need

dare

used to

ought to*