In the Canvas dashboard, select the course you would like to add zyBooks as an external tool (you will only have to do this once and the tool will be available for all future classes).
Click "Settings" and then click "Apps".
Search for "zyBooks" in the search bar.
After selecting zyBooks from the search results, click "+ Add App" and you should see the following form:
Contact email@example.com with the name of your institution to receive the consumer key and shared secret.