When you are creating an assignment you can choose whether the assignment is handed in as an individual or a group.
If you choose to have a group hand in, select the group option. You will then have to choose a maximum group size by using arrows.
What does this mean for students? Only one student from a group hands-in, this student will choose the option to upload as a group and then select the names of the other students in their group. All group members will be notified that their hand-in has been submitted.