You can add new users to your Filr site in any of the following ways:
LDAP:
Synchronize newly-added users from an LDAP directory, as described in LDAP Servers and Synchronization
in the Filr 3.4.1: Administrative UI Reference.
Local: Add local users and groups, as described in Managing Users and Managing Groups in the Filr 3.4.1: Administrative UI Reference.
Profile Files:
Import XML profile files to add and manage local users and groups, as described in Import Profiles... button
in the Filr 3.4.1: Administrative UI Reference.