Big name for a very basic idea: pointing out which thing or things we're talking about. In English, we use this and these, that and those. Pretty simple stuff once you get the hang of it. Here are some resources to learn more.
Gramactiva video: Demonstrative Adjectives
Practice with Demonstrative Adjectives
Online activities from the Exprésate textbook
Self-correcting exercises
Videos and interactive activities to learn Spanish online
Detailed grammar explanations with self-correcting exercises
Grammar explanations with self-correcting exercises
Excellent grammar explanations with video
Online Grammar Lessons with worksheets
Pinterest: Demonstrative adjectives
Music videos to help you learn!