Some examples of demonstrative adjectives would be the following:
Have you read this book? (notice “this” is an adjective because it describes the noun “book”)
Please hand me that pencil. (notice “that” is an adjective because it describes the noun “pencil”)
Did you intend to purchase these packs of gum? (notice “these” is an adjective because it describes the noun “packs”)
He wanted to bring those gifts to the party, but he didn’t. (notice “those” is an adjective because it describes the noun “gifts”)