Did your course syllabus list books you need to buy?
The bookstore is where you want to visit for all of your textbook purchasing needs.
Visit the online bookstore. Use their contact info here. The bookstore will show you required book purchases for your courses and also allow you to use any vouchers or credits you have. If you want to see if the library happens to have a copy you can use of the book, look in Primo search and then narrow the search to "online sources" or "held by library in print."
Sometimes, professors will link required readings in the modules of the course. Look through your modules to see what is linked. Other times, they will use the "Reading List" tool in Canvas. Look in your syllabus and the left menu of your Canvas course to see if there are readings linked there. If the professor told you to find a source at the library, look for it in Primo search.
If it is a required purchase, you can buy it through the bookstore (above) or find a copy online to purchase. Search for a "used" copy to save money. On occasion, an older digital version of a textbook may be available on the internet.