You have probably used books to help gather information before. If you think about what made books a useful resource, it was likely that the book gave you an in-depth overview of your topic. The author was able to talk at length about the issues and could provide a lot of background information. Because books are usually fairly lengthy, the author will probably discuss other things besides your exact topic. When this is the case, it is a good idea to use the table of contents or the index to go just to the parts of the book that are relevant for you, rather than reading the whole book.