1 'This' is used to denote a singular thing and 'these' are used for plural ones. This/these help to denote something or someone that is near us or could even be used as an introduction. In short, they are used to display the relative distance between the speaker and the noun.

Example:
a. This is my house.
b. These are our friends, Janet and Robin.

2. 'That' is used in singular circumstances and 'those' are used in plural scenarios. It is used to show something at a distance.

Example:
a. That is my house.
b. Those are very expensive cars.

3. This, that, these and those are demonstratives. We use them as determiners and pronouns.

a. That water tastes strange. (determiners)
b. I might get myself a pair of those shoes.(determiners)
c. Come and look at this.(pronouns)