What they are and what they can do for you
Books can go broad and deep because they are long. Use a book to get a combination of ideas, numbers, history, theory--a book can do it all. But the publication cycle can take 6 months to many years, given the time it takes to research, write, edit, publish, print and deliver books, so don't expect a book to cover the most recent ideas. Note also their bibliographies (and those references found at ends of encyclopedia articles) for related works on your topic.
Books might be popular or scholarly, so use your critical thinking skills to evaluate books, even if you do get them from a library.
Find books and e-books in the McDonald Library collection
Google Books searches a huge library of digitized books. You can get full-text of those books out of copyright domain, i.e., 70 or more years old. You can get partial full-text some current books, and sometimes there is no full-text, but all the books are linked to a library or a bookstore.