To find books written about a specific person, do a Subject search in OSCAR (the library's catalog) and type the person's name (last name first).
If you are looking for books about a topic (not a person), do an Advanced Search in OSCAR. If the first terms you type do not give you the results you want, try typing in various ways of describing your topic. Then, once you find some books that look like what you want, click on the Subject links that appear in the full records for those books, and you will probably find even more books on the same topic. (For example, if you type "Roman aqueducts," you will find a few books, but clicking on the Subject heading "Aqueducts -- Italy -- Rome" will reveal additional books to choose from.)
Your results will probably include printed books that can be found in the library building, as well as electronic books that can be read online. You can tell which books are printed books because a location in the building is indicated as part of its record in OSCAR. E-books have no physical location indicated, and the words "(Electronic Resource)" usually appear immediately following the title of the book. Click on the title of the book to open its record in OSCAR; then click the link in the middle of the screen to read the book online.