What are books anyway?
When doing research, you can find a lot of information about a topic in books. Books are different than articles because of their length and level of depth.
Books are much longer than articles. Because of this, books usually address many different aspects of a topic and don't focus specifically on one certain thing. The important thing is to think big when searching for books. For example, if you are interested in violence in video games, you're not likely going to find a book just about violence in video games. But you will definitely find books about video games as a whole, and then you can find specific chapters or sections in that book which addresses violence in video games.
Books treat subjects in great depth. They can discuss a topic academically, and/or historically, and/or in terms of how it affects society in everday life. Because books are long and focused on broad topics, each chapter or section will address a smaller component of the topic.
Why use books?
One reason to use books when doing research is because you know that the person who wrote it knows what they are talking about. Years of research and work can go into writing a book. They are authoritative. Use books because the ideas in them really put your topic into perspective.