All of the libraries have printers that you can use to print from either library computers or your own. Detailed instructions can be found on the Printing Instructions page.
Be sure you have Duck Bucks on your UO ID card or generic print card. Add money to your Duck Bucks account online with a debit or credit card, or use the cash-only card machine in the lobby of Knight Library or at the UO Card Office (ground floor of the Erb Memorial Union).