Demonstratives: This, these, that and those

 Demonstratives are used to point to objects that are at a short or far distance.

This 

It's used for a thing that is close. (singular)

For example: This marker is blue.

These

It's used for things that are close. (plural)

For example: These markers are blue.

That 

It's used for a thing that is far. (singular)

For example: That marker is blue.

Those

It's used for things that are far. (plural)

For example: Those markers are blue. 

This apple is red. (close and singular)

These apples are red. (close and plural)

That apple is red. (far and singular)

Those apple are red. (far and plural)

Notice!

"is" is for a singular noun.

"are" is for plural nouns.

Here, we have a video of this:

Now, we have a Quiz to practise.