Refence books can be found on the main floor of Olin, to the right when you enter. They cannot be checked out, but that means they are almost always available, and they can be copied.
Reference sources are a good place either to retrieve facts and numerical data, or to get an overview of a topic in a few paragraphs or a few pages. Looking up a topic in a reference book is an excellent way to familiarize yourself with the key concepts, terminology, and people associated with the topic. This background is important both for understanding a topic and for searching effectively in online databases for articles and books. In addition, many reference works provide carefully selected bibliographies which may lead you to further reading.