In order to understand the difference between these two terms we need first to understand the difference between this and that, since these is the plural of this and those is the plural of that.
The most basic difference refers to the distance of the object to the speaker. You should use this when the
object is close to the speaker, and that when it is away.
For example:
This is my book. (a boy points to a book on his hand)
That is your book. (a boy points to a book close to his friend)
Similarly, if you the things are close to the speaker you should use these, and if they are away you should
use those.
Notice that the time will also influence the usage of this and that as a demonstrative pronoun. If something
happened in the past, the usage of that is more appropriate.
For example:
He didnt go to the school. That made me think.
If the event has not happened yet, on the other hand, this is the correct form. For example:
He wont go to the school today. This is quite strange.
Finally, a bit of trivia. When Americans answer to the phone they often say Who is this?. While in the United
Kingdom people will say Who is that?