Click on the How to give access to different files to different students 1 icon and then click on the All option.
How to give access to different files to different students 2

Add, copy and paste, drag and drop the files you want to each of the six possible group playlists A, B, C, D, E and F.
Students in each group will see different files in their corresponding playlist area. The image below shows the playlist for a student in group A – they double click the file(s) to open.
How to give access to different files to different students 3