These is a word we use to point out specific things or people that are nearby or that we're currently talking about. When you hold up two books and say “these books are my favorites,” you're indicating exactly which books you mean: the ones right there in your hands.

The word helps us be clear and specific. If you walk into a bakery and say “I'll take these,” pointing at the chocolate chip cookies, everyone knows exactly which treats you want. Compare that to saying “I'll take those,” while pointing across the room at the oatmeal cookies instead.

These is the plural form of this. You'd say “this cookie” for one cookie nearby, but “these cookies” for two or more. The opposite word is those, which points to things farther away: “I like these shoes I'm wearing, but I also like those shoes across the store.”

We also use these to refer back to things we just mentioned: “Some students stayed late to help clean up. These students showed real responsibility.” Here, these connects back to the students we just talked about, making it clear we mean that specific group.