When your class/group is done, you may want to archive your channel so that it is removed from any directories and cannot be used anymore. Archiving will make it so that nobody can be added/send messages, but you as the owner will still be able to search for it and find it in case you want to read through the previous messages.
If you want to fully delete the channel and all of its messages/content permanently, let us (Nectir admin) know and we will do it for you.
To archive your channel (you must be the owner of it):
Click the "i" info button in the top right corner of the channel.
Click the "Edit" button.
Scroll down until you see a toggle button that says "Archive" next to it.
Toggle this on, press "Save", and your channel will be archived! You can go back and un-toggle it at any point to bring the channel back to life.