The required course textbook is an interactive online zyBook that offers a number of advantages over static text-dense textbooks. It will be available through the UCLA Store's Bruin One Access (for undergrads) or Inclusive Access (for grads) program.
Some of the interactive activities will be required assignments. If you have any questions/issues about administrative aspects of zyBooks (access issues, etc.) contact support@zybooks.com or look at the Students section at the zyBooks help center.
(By the way, if you are having enrollment problems with CS 31, see https://cs.ucla.edu/classes/enroll/31/.)