How can I set up my Friend Safari?
On your 3DS home screen, there is an orange blocky smiley face near the top. That is your list of 3DS friends. Every person with a 3DS has a unique friend code, and two people who add each other as friends using these codes will show up on each others' lists.
After you beat the Elite Four, you get access to the Friend Safari in Kiloude City. Every mutually added friend on your friend list will have a specific type and 2 - 3 set Pokemon of that type tied to their name. All friends, even those who don't have Pokemon, will have a type and 2 Pokemon. Those who do have Pokemon tied to their 3DS friend code and who have also beaten the game / been to the Friend Safari will then have 3 Pokemon tied to them, and there is a higher chance of the Pokemon found there having their hidden abilities. Every time you have a mutually added friend, they will immediately show up as an option in the Friend Safari.