These and those are both pronouns, words that substitute for other nouns in a sentence. Knowing when to use each pronoun can be tricky, however. If you're confused about when to use these and those, read on to find out the difference between them.
These and those are both pronouns, words that refer to or substitute for other nouns in the sentence. They draw attention to something specific. Because a pronoun takes the place of another noun, using the correct one helps your reader understand what the referent of the pronoun is (what noun it took the place of). We always think that the These and those are plural pronouns: they refer to or replace plural nouns.
These is the plural form of this. You will use it to refer to or replace a plural noun.

Singular: This book (a single book) on the shelf next to me belongs to Rajeev.
Plural: These books (several books) on the shelf next to me belong to Rajeev. [Note that the verb belong has also been made to agree in number.]
Singular: Look at this bracelet (a single bracelet) on my wrist!
Plural: Look at these bracelets (many bracelets) on my wrist!
Singular: Who put this cupcake (a single cupcake) in the refrigerator?
Plural: Who put these cupcakes (some cupcakes) in the refrigerator?

Those is the plural form of That. You will use it to refer to or replace a plural noun.
Singular: That mountain (a mountain) looks really small from here.
Plural: Those mountains (several mountains) look really small from here. [Note that the verb look has also been made to agree in number.]
Singular: Could you hand me That box (a box) on the other side of the room?
Plural: Could you hand me those boxes (a few boxes) on the other side of the room?
Singular: Why hasn't that scientist (a scientist) at NASA found extraterrestrial life?
Plural: Why haven't those scientists (many scientists) at NASA found extraterrestrial life? [Note that the verb have has also been made to agree in number.]