Select the Assignments tool from the Tools Menu in your site.  

Note: You can only select the group submission option for a new or draft assignment. Once the assignment has been posted for students, you cannot change this setting.

If you select the Display only to selected groups option, the settings will expand to show a list of all existing groups in the site.  Select one or more groups to display the assignment to those groups only. If you selected the Group Submission option, you may limit the groups that are allowed to submit here.

Note: The display option only controls the visibility of the assignment for users in different groups. By default, each member of the group still submits an individual assignment, but this display setting allows you to identify different assignments for different groups or sections.

Tip: If you want students to submit one assignment per group, use the Group Submission - One submission per group option below.

If you select the radio button for Group Submission - One submission per group it will allow any member of a group to submit an assignment on behalf of the group. By default, the same grade is applied to all group members when the item is graded. However, the instructor can also override the group grade for any individual member of the group.

Note: You must have existing groups in your site in order for the group option to appear.

Once you have entered all of your assignment settings, scroll down to the bottom and click Post to save your changes and post the assignment.