There are instructions on the website, but basically you change the DNS setting on your DSI so that when you go to the GTS (global trade station) it directs your DSI to that website vs the offical GTS website. Do you know how when you upload a poke to trage on the GTS then when you come back and it has been traded, the new poke falls out of thesky into your DSI? That is what happens.
Try it.