sync in global link in the game. Follow the steps. After you register at the global link website you will be able to exchange items for the poke miles. Poke miles are earned by walking, trading (including wonder trade), battling, and streetpass. :)
With the release of the Generation 6 Global Link, they still have another section to open, which I assume is the Dream World equivalent which was available on Generation 5 games ^.^ Attractions are a new feature that will be within that I assume :3 Here's more information about it xD
You can also get a few pokemiles via streetpass which would work great at cons. So far all we can do with them is to buy rare potions both in game and on the pokemon global link website but hopefully the attractions section will open up and we can play mini-games for free stuff!