From the birthdays page you can add in address info about the friends you'd like to send cards to.
You can choose which card template gets automatically sent on the Settings Page
A few things to know about this feature:
-- It can take a few minutes for the chrome extension to sync w Facebook, so just leave chrome open while this is happening.
-- Only the birthdays of Friends who allow their bday info to be shown will be synced.
-- Cards will be sent automatically as your friends birthday's come up, and they'll think you're AWESOME!