To have your students join via class code go to the Participants page of your class. Located at the top of the Participants is the class code.
Display the class code to your class by clicking on the arrow next to the class code and select Show code to class.
If you would like to turn off access to the class code click the arrow next to the class code and select Deactivate class code. Students will no longer be able to join with this code.
You can reactivate a new code - this is a new code that will need to be shared again with students.