Your professors sometimes will put items "on reserve" for use by students in particular class. Such items are available to be checked out for a short period of time (usually two hours or one day), so that as many students as possible are able to use the item.
Items on reserve are available at the Hiebert Library circulation desk. They are shelved by the course name and number, so that and the book's author is the most helpful information to provide when asking for an item from the reserve shelves.
You can check to see what items have been put on reserve by a particular professor or for a particular course by checking the library's discovery service. Enter the name of the professor, the name of the course, or the number of the course. The results may include some items not actually on reserve, so you can focus your search results by looking at the gray "Refine by" box on the left side of the results screen. Scroll down that box until you find sections for "course" and "professor" (see example below).
Clicking on those links will show a list including only reserve items for that course or professor. All items on that list can be requested by coming to the circulation desk.