We use THIS / THESE for things near us. We use THAT / THOSE for things far away from us.

We use THIS when something is close and there is one object. For example: This is a book in my bag.

We use THESE when something is close and there are more than one object. For example: These are the books in my bag.

We use THAT when something is far and there is one object. For example: That is a big tree on the next street.

We use THOSE when something is far and there are more than one object. For example: Those are big trees on the next street.