Obtained in: Inherent ability (Only usable once you join a faction)
Command: /delegatefactionpoints [client] [amount of FP] (/del can be used as a shortcut)
Effect: The amount of faction points specified are transferred from you to the specified client.
For a full guide to becoming a faction broker, see Devyn's brilliant:
The Smuggler's Guide to Selling Faction Points
His guide has a full table on how much it costs to buy faction points at your faction rank, as well as details fo the peculearities that often confuse people.