Demonstrative pronouns show which person or thing is being referred to.
This, that, these, and those are demonstrative pronouns.

In a sentence, a demonstrative pronoun is commonly followed by a verb.

This is singular. It refers to something that is near.
➜ This is an apple. 👉🍎

The demonstrative ‘the’ is used because there is one apple, and it is near.

That is singular. It refers to something that is far away.
➜ That is an apple. 👉     🍎

The demonstrative ‘that’ is used because there is one apple, and it is far away. 

These is plural. It refers to something that is near.
➜ These are apples. 👉🍎🍎

The demonstrative ‘the’ is used because there are two apples, and they are near.

Those is plural. It refers to something that is far away.
➜ Those are apples. 👉      🍎🍎

The demonstrative ‘the’ is used because there are two apples, and they are far away.

Demonstrative pronouns can also be used as demonstrative adjectives when describing a noun.
In a sentence, a demonstrative adjective is commonly followed by a noun.

For example:

➜ That apple is red.

➜ This apple is red.

➜ These apples are red.

➜ Those apples are red.