Modal verbs are used for ideas and possibilities. Modal verbs in English are auxiliaries: we put them with other verbs.
She can speak three languages.
It could rain tomorrow.
I must go.
In these sentences, we put can with speak, could with rain, and must with go.

The three most common functions for modal verbs are ability, probability, and obligation.

She can speak shows ability: she has the ability to speak.

It could rain shows probability: the chance of rain is small.

I must go shows obligation: I have a need to go.

An auxiliary verb is a verb which we put with another verb.

We use (do) as a finite auxiliary for questions and for emphasis. Do is followed by an infinitive.
Where did she go?
I do play tennis, but I do not play squash.
Note that we use “do” with most verbs, but never with forms of “be”.

We use (modal auxiliaries) as finite auxiliaries for ideas and possibilities. A modal auxiliary is followed by an infinitive.
I should go.
Can you help me?

We use “used to” as a finite auxiliary to talk about past habits. Used to is followed by an infinitive.
He used to play hockey, but now he plays golf.

We use (have) as a finite or non-finite auxiliary in (perfect form) verbs to talk about something before the main time. Have is followed by a past participle.
I am not hungry: I have eaten breakfast.
She needs a bandage: she has grazed her knee.

We use (be) as a finite or non-finite auxiliary in (continuous form) verbs, followed by a present participle, to make the verb stronger.
He cannot answer the phone: he is doing an exam.
At 3 p.m. yesterday, they were sleeping.

We also use (be) as a finite or non-finite auxiliary in (passive form) verbs, followed by a past participle, to talk about an action which affects the subject.
This play was written by Shakespeare.
Hyundai cars are made in Korea.

The present participle of a verb always ends with “-ing”.

The “-ing” form is not finite: it does not change for different people or different times.
I was swimming.
She is swimming.
They are swimming.

The past participle of a verb can end with many forms, including “-en” (or “-ne”), “-ed”, or “-t”.
eaten, done, finished, learnt

The “-en/ed/t” form is not finite: it does not change for different people or different times.
I was seen.
They were seen.
She is seen.

The past participle is not a verb by itself. Instead, it is an (adjective) or (adverb).
The book taken from the desk was mine.
Broken in the storm, the door hung loose.
In the first sentence, taken is an adjective: it modifies the noun book. In the second sentence, Broken is an adverb: it gives the reason for the verb hung.

The past participle can become a verb when we put it with an (auxiliary verb).
With “have”, the past participle forms a (perfect form) verb.
I have eaten two of those this morning.
She has done her homework.

With “be”, the past participle forms a (passive form) verb.
That photo was taken in Rome.
The meat was frozen in the freezer.

The infinitive of a verb is not finite: it does not change for different times or different people.
I want to try.
She wants to try.
They wanted to try.

Every English verb has “finite forms”. These are the forms which change for different people or different times.
I like coffee.
She likes coffee.
He liked coffee when he was young.
We only use like for the past, not for the past, and only with I or you or we or they, or with a plural noun subject. We only use likes for the present, not for the past, and only with the pronoun subjects she or he or it, or with a singular noun subject. We only use liked for the past (e.g., when he was young), not for the present.

When a verb has more than one word, the first word is always a finite verb.
The window was broken.
He is sleeping.
They are going to win.
In each of these sentences, we must change the verb if we change the subject from singular to plural, or from (third person) to (first person) or (second person), or if we change the time.
The windows were broken.
They are sleeping.
They were going to win.
The other words in the verbs do not change because they are not finite.

A verb shows an action or state, what something does or what something is.

Most English verbs have four parts:
1. finite forms, which change for different times or different people (e.g., am, is, are, was, were);
2. infinitive forms, which do not change for different times or different people (e.g., be);
3. -ing forms, which always end in “-ing” (e.g., being);
4. -en/ed/t forms, which end in “-en/ed/t” (e/g/, been).

Different verb types need to be followed by different things. Some verbs are followed by a noun object. These are called “transitive verbs” (from Latin trans, “across”, +it, “go”, i.e. the verb “goes across”, like a bridge, from the subject to the object).
I heard a noise.
She saw him.

Some verbs are followed by an adjective. These are called “complement verbs”, because the adjective is not an object and so is called a “complement”.
That smells good.
I feel happy.

Some verbs do not need anything after them.
We slept.
The accident happened.

The grammatical difference between verbs like see and look, or hear and listen, is that one needs a noun object and the other cannot have a noun object, but we can add a prepositional phrase to both of them.
He looked through the window. He saw me through the window.
She heard voices. She listened to the words.

We use different verb forms for different times.

A noun is a name for something.
cat, desk, disappointment, France

We can replace a noun with a pronoun.
Can you see my phone? I need it.
Sam is here. Yes, there she is.

In a clause, a noun can be the subject, or the object of a verb, or the (object of a preposition).

The three main groups of nouns are countable nouns, uncountable nouns, and (proper nouns).

Common noun endings:
reality, nation, kindness, confidence,

We use an uncountable noun when we want to talk generally about something, and not about one particular example.

As a result, we use uncountable nouns for groups.
I have found all of the equipment: a net, two racquets, and several balls.
Because so many people buy cars, there is too much traffic on the streets.

We also use uncountable nouns for things which do not have separate parts because every bit is the same.
All water is water. All air is air.

However, we can change countable nouns into uncountable nouns if we want to talk about the general idea, not a specific example.
Bob: Do you want a chocolate?
Sam: No, thanks. I can’t have chocolate.
Bob: Would you like an ice cream, then?
Sam: Absolutely! I love ice cream.
A noun becomes countable or uncountable depending upon how we use it.

Countable nouns are things which we can separate:
This pen is not the same as that pen.
Quick, give me a phone! Any phone is okay!

If a countable noun is singular (i.e. just one), we must put a [determiner] before it:
my phone, her phone, this phone, that phone, each phone, every phone
Countable, singular nouns are the only type of nouns before which we can put a or an.

If a countable noun is plural (i.e. more than one) or if a noun is uncountable, we do not have to put a [determiner] before it. This is one way to recognise a countable noun.