Go to the library homepage and click on "course reserves" beneath the search bar. Key in the professor's name or the name of the course. Find the number of the book you want.
For example, if the book is Gardiner's Art through the Ages for Prof. Inwood, the number is I1. Go to the help desk with your ID and ask for I1. They will check it our to you for 2 hours (or the time allotted by your professor).