Hi @JuliaTheis !
Thank you for posting on the instructure Community.

To locate your join code for the class, please navigate to your course settings, then scroll down under the course details tab until you see the button that says Let students self-enroll by sharing with them a secret URL or code. Once enabled, click save and then refresh your page and the code will be displayed.

I will provide a visual here to help you out if necessary: https://ptsd.instructuremedia.com/embed/6caf3e5d-cf9d-4388-b955-d7a923b75502 

Hope this helps!