You can buy your books, clicker, and other suggested course materials at the on Main Street or at any of the bookstores in downtown Newark. The bookstore offers the option of renting some textbooks and choosing used copies of others if you prefer, which can cut down on your costs.
If you order your books online through the UD Bookstore, the ordering system will indicate required books for your course and section. If you want to buy your books in person, take a copy of your schedule with you to the bookstore and the staff will help you get the books you need for each course. The correct books will also be noted on the syllabus for each course. Note that some books are required; you definitely need to purchase those. Other books are recommended, so it is up to you whether you want to buy those titles.