This and these are for people and things near us.
This (singular) and these (plural) are pronouns.
This apple is delicious. (Apple is singular)
Whose keys are these? (Keys is plural)
We also use this and these to introduce people.
This is Mr. Thomas.
These are my friends, Anna and Juan.
That and those are for people and things that are not near us.
That is a singular pronoun and those is a plural pronoun.
That car was speeding. (Car is singular)
Who are those people over there? (People is plural)