From a Filr perspective, users can get the required permissions to access files and folders in one of three ways:
Directly: Users are assigned permissions to the files and folders.
Group Membership: Users inherit permissions to the files and folders through membership in a group that has been assigned the permissions.
Net Folder Proxy User: Users receive and accept Filr share invitations. They can then access the shared files and folders through the assigned Net Folder proxy users that have the required file system rights.