By default, any active member of the platform can create a group. However, this can be restricted to manager/admins by the Super admin under the Access Control Settings.
To create a custom group,
New Group in the navigation menu under Connect
Click on the
CREATE GROUP button on the right side of the View all Groups page.
Complete the details.
Configure the member access rights.
Create the group.
There is no option to delete a group, but it can be archived and appear at the bottom of the joined group list.
Once all the group members leave the group, it gets automatically deleted.
The process to add Group members is here.