When a course is over you can archive it. Archiving a course makes it read-only for students, but still allows you and students to access data in the course.
How to archive a course
To archive a course, navigate into the course, press the context menu icon in the top left corner shown on top of the course thumbnail. In the context menu choose "Archive course".
Seeing your archived courses
Your archived courses are listed under "Archived courses" on the page where you can see a list of course.