A group admin is a position that any member of the group can be assigned. A member does not need to be the leader of a group to be a group admin.
See here for how to update a member's position.
A group admin has the following abilities with their group:
Can send e-mails to groups members through the member listing page
Can upload and delete group files
Can start group discussions
Can delete group discussion threads and messages
Can see notes inside a group
A group admin canNOT:
CanNOT edit group details
CanNOT delete groups
A group admin is easily identified from the member listing with the admin banner.
A leader will also have the admin banner over their image in the lower left-hand corner of the group page.
NOTE:
A group admin will also have these permissions over any subgroup under the group that they are an admin of.
If the membership of a group is set to "Approval Required," group admins are emailed to decide whether the person should be approved or denied membership.