We use this (singular) and these (plural) to refer to something that is here / near.
- This is my car. (singular)
- These are our children. (plural)
We use that (singular) and those (plural) to refer to something that is there / far.
- That is our house. (singular)
- Those are my shoes. (plural)
Note that the verb changes (i.e. singular / plural) depending on the pronoun that you use.
You can also use Demonstrative Pronouns by themselves:
- Did you do that?
- I’d like to buy these?
- Which of those would you like?