There are two basic ways to find books in the catalog: one is to throw a search into the box on the Libraries main webpage and hope for the best. This search is called a "Discovery layer" and is great for a quick search, but you will get a lot of information that way, and you will need to use the filters on the left side of the page to narrow your search. This feature is meant for undergraduates with little experience using the library and a lot of experience using Google.
A more sophisticated search can be done by using the library catalog. This search will pull up mostly books, but you will also see videos, streaming film, sound recordings, and even maps. What it won't pull up are journal articles or newspaper articles. It is important to note that this catalog search does not search the content of the books, so you have to think broadly when you search. For example, a search about refugees after world war II would be a keyword search for "refugees and World War and Europe." If you are too specific in your search, you will get bad results.
In ALL cases, if you need help finding books, the Reference Desk is a great place to start (1 east, near the Circulation Desk). The librarians and staff at that desk can help you with your search strategy to find books or articles you need.
Journal Article Indexes are databases with citations and sometimes full text of journal articles. Many times, these indexes are subject specific, so that they only search the journals in the History field, for example. Using these are a very efficient way to find secondary sources. Remember to keep your searches very broad to start, then add in words to narrow them down. Also be aware that these indexes often cite materials in other languages, though their abstract may be in English. If the title of the article is in another language, it is a good bet the article itself is as well.