Use books to find historical information, in-depth research on a broad topic, tables of scientific information and more. Books can provide introductory and comprehensive information on your topic. Books are great sources because they have been rigorously edited and fact-checked before they get published. You will find high quality information in books. One thing to watch out for is the year the book was published; some books may not be current enough for your topic.
Google Books is another good place to look. For some books you can read the entire book. For others you can see a preview of the inside of the book.