Snapshots are screen shots of students' screens. You can take these on the Individual student page and the grid thumbnail view on the Session tab, and then you can see all of them on the Snapshots tab. If on the grid thumbnail session view, you see that a student has something else open other than the Chrome browser and you click Take snapshot, Classroom Manager takes a snapshot of the whole desktop. You can see other open windows that are in front of the browser, for example, if they have their web camera video on.
You can download all of the snapshots in a single zipped file or download a single snapshot image. Once your session ends, all of the snapshots that you have taken during the session are deleted and you can't retrieve them. Therefore, it's recommended that you download and save any snapshots that you might want before your session ends.