When creating a group, you can select Enable external access
to turn a community group into a place where standard users can invite external contributors
to extend their communication and collaboration to the outside world.
To create a group with external access:
Click > Group.
On the Create group page, enter the group name and details.
Select Private or Secret (also known as Private: Unlisted) for the group type.
External groups are limited to Private or Secret (Private: Unlisted) groups to
help protect community information.
Select Externally Accessible to allow external
contributors to be invited to and join the group. Externally Accessible groups
must be private or secret (also known as Private: Unlisted). You may not see this option if it's not enabled for your community.
Click Advanced for more options.
Click Create Group.
If you see the Invite People to Join dialog, then add a few users who you want
to invite to the group, and click Send Invitation.
To manage group features and select the storage provider, select gear icon > Configure activity page
Click the gear icon in the Enabled Features and Content Types tile.
Select or unselect features for the group. People will be able to create the
kinds of things you select.
If available, you can select a storage provider for storing your uploaded files.