You can use the SLU Libraries Catalog to search the library’s collection and find call numbers and locations. Additionally, the library catalog will allow you to see if the library subscribes to specific journal titles and whether that subscription is for an online copy, a print copy, or both.
The SLU Libraries Catalog is usually the best place to find books in Pius Library and ebooks online. I recommend starting your search with keywords and using the Subjects listing towards the bottom of the individual book record to find similar titles. For example, if you were looking for books on engravings by Albrecht Durer, you could try using the terms: Albrecht Durer and engravings (using the word 'and' in between your search terms will help manipulate your search results, so I highly recommend it). Or better yet, you could use the terms: Albrecht Durer and prints, since prints is a broader category and will include engravings. And, if you use the Subjects listing towards the bottom of the book records, you can quickly discover all books in the library on the subject of Durer using the link, Dürer, Albrecht, 1471-1528.
Last, a quick note on searching for books on architecture or art that is specific to a site (like stained glass). Always use the location in your search, city or town. For example, if you wanted books on the cathedral in Reims, France, you would want to use search terms like Reims and Notre-Dame. If you just used the terms, Notre-Dame and architecture, you would come up with hundreds and hundreds of results since there are many churches with that name. Most buildings get classified by their location before their name.