As the Vibe administrator, you need to enable sharing privileges for users on your Vibe site before users are able to share files and folders from their personal workspace. You then need to enable sharing for the top-level Global and Team workspaces in order for users to be able to share content from those workspaces. You or workspace owners can then enable sharing on lower-level workspaces on an individual basis.
There are various sharing privileges that you can grant.