When students have submitted activities, they'll initially be visible only to you as the teacher, and to the student that submitted them, within the Activities section. This means that you can provide formative feedback in a confidential forum, or request resubmission if necessary.
Once all submissions have been reviewed, the activity will be marked as Reviewed, and you'll be prompted if you are ready to mark it as completed.
Remember, even if an activity is past the due date you've set, students can still submit responses. Submissions after the due date will be flagged.
When you're ready to fully close down the activity, that's when you can use the Mark Complete option. This can be accessed either on the main activity screen for an activity that has been fully reviewed, or through the menu button (three dots) on each activity.
After clicking to mark the activity as complete, you'll see a confirmation dialog where you can decide whether or not to publish your students' submissions.
Note that marking an activity as complete is irreversible, so make sure that you're really ready before clicking Yes. You can still make a copy of the activity and assign it again to the same class or another, but the copy will be separate from the original.
There are two options for publishing content, and both are enabled by default:
Publish completed activities to this Space
If this is turned on, your students' submissions will be turned into posts in the Space once you mark the activity as complete.
Posts will be visible to other students, or not, depending on the Space Settings that you have applied.
Include comments in published posts
If this is turned on, any comments that were added by students or teachers within the activity submission will be included as part of the published post.
Whether or not the comments are visible to other students will depend on the Space Settings.
If you prefer to keep this dialogue private, you can disable this option and the comments will not be included with the posts.
Once the activity has been marked as complete, it will be moved over to the 'Completed' tab for teachers and students. Activity instructions will remain visible, but from that point on, students will no longer have the option to submit responses for the activity.