How do you get a friend code in Animal Crossing: New Leaf?

To get their friend code, go to the "Friends List" on the top of the bottom screen. It will be a slightly rounded square, which will be orange and have a smiley face. Once you open the application, press the "Register Friend" button. If you are next to your friend's 3DS, you and they can press local. If you want to exchange friend codes from far away, you need to both look at the card that says your name, give each other the faint letters shown with the "-" marks in between (your friend code) and then go to register friend and then press "Internet". both people need to have each other's friend code.