For newcomers/first-time players, this thread is basically exactly what it does: serves the purpose of making it easier to gather friend codes.
Remember, the main purpose to Friend Codes in this game is for the Friend Summon function. I highly suggest updating your Friend Summon relatively frequently to make yourself helpful to other players.
An additional function to Friend Codes serve for the Abilink feature. This allows you to Abilink ("ability link" -- exactly on the tin) a friend's job levels to your party members. Essentially. it allows you to access higher level skills from a class without being at that level yourself.
And no, they do NOT count to your villager population. Villagers only count via streetpass and daily Net-Invites. Adding people by Friend Code does not do anything relating to your village.
FC database http://goo.gl/4vMPxe
FC submission form http://goo.gl/YI5XZz
I highly advise to PM the person you have added since there's no other feasible way to let them know