UBorrow is an agreement between the libraries in the Big 10 to share books. The reasons to use UBorrow include quicker average delivery times and a longer loan period than traditional ILL.
The benefit of using WorldCat is that it provides you with access to even more materials held at thousands of libraries.
If a book is not available through UBorrow your next step is to request it through Interlibrary Loan. Follow the Interlibrary Loan link available here and log in when prompted.
Another way to place an ILL request is through WorldCat, a tool that searches thousands of library catalogs at once. When you find the book you need, click on the "Request via ILL" link for an easy way to place an interlibrary loan request.