Most books available online (for free) are older titles - published before 1923 and in public domain.
The Libraries search interface will search the collections of all libraries on campus, including eBooks. Search results will tell you where physical books are located, and if they're available to check out.
If the Libraries don't own or provide online access to a book or article you want, log-in to InterLibrary Loan (ILL) to request the book from another library.