How exactly do we trade with the GTS?

My friend and I are trying to trade each other's starters, and we can't seem to find each other in the GTS system. We can fight each other's virtual trainers just fine, but trading.... we can't! We've tried using our online IDs, and our pokemon's IDs, and neither of them seem to work. We've also tried making sure we have different IP addresses. Is it simpler than we think it is, and we're just missing something? or do we have to be further along in the game? (He's just gotten the first badge and I've just gotten the second.)

Have your friend put up the starter on the GTS asking for yours, then you can search for it using Search by Wanted. There arnt to many people who are trading at the moment so if your fast you wont have any trouble. Also Make sure to input your ID correctly As well. Including the 0's