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Have an officer in the student organization log into their SUMail account via a web browser.
At the very bottom of the student's mail folders, there should be a Groups folder that when expanded shows a link that reads "New Group". Click that link.
In the "New Group" dialog box, enter a name and description for the new group. Keep the Privacy setting set to "Private" so only organization or club members can see emails sent to the group.
Click the "Create" button to create the group. The creator of the group can then
add other organization members
set owners of the group
invite others to join the group
specify whether someone outside the group can email it
control whether members receive all email communications to the group email.
For further details on these options, refer to the Microsoft article on Office 365 Groups.