These are the demonstrative adjectives, that usually come after nouns (singular and plural) to demonstrate them, showing as well the distance you are from those things.
We use this (singular) and these (plural) for things that are near us:
This shirt was cheap.
These shoes are new.
And that (singular) and those (plural) for things far from us:
That plane is going to Europe.
Those bananas from the market are the best.
They can also become demonstrative pronouns, being used in a similar way as the demonstrative adjectives, but now with no need for a noun. Of course context is needed in this case:
(The food) – This is delicious! Congratulations!
(The books) – These smell like new.
(A noise) – Did you hear that?
(Paintings) – Who painted those?