Books can be great sources for your research. They:
Provide broad overviews of a topic
Put your topic in context with other issues
Discuss big ideas or issues
Reading from books can make it easier for you to understand academic articles on the topic.
No, not usually. Just read what is useful to your research. You can start by reading the introduction of a book and any relevant chapters.
All library books have subjects assigned to them. Subjects are a bit like hashtags in that they group books on the same topic together. Once you've found one book on a topic, click on a subject to find more on that topic.