First you must have a wireless connection spot available (or a DS Wi-Fi USB key, they don't come cheap though).
You must run the Wi-Fi configuration from the menu (I can't remember if game menu of DS menu) and configure it. How to do this depends on the kind of connection you have and if you don't know how to, then you should ask to those who set up the router first.
Then you will use the Moogle mail to connect to the Nintendo Wi-Fi connection (you must choose to send a message to a faraway friend) and by doing so you'll get a Friend Code. Now exchange Friend Codes with a friend and start sending Moogle Mails to each other (you'll only see each other in the Friend List when you both connect at the same time after exchanging Friend Codes.

If you haven't done this I suppose you haven't done the Oricalc quest yet nor the hidden boss.