Turn on your DS system and go to Settings. Then go to the tab that says Internet. Click it and click the next one that says Commutation Settings. There should be thee numbers 1-3 click one of them and click find connection. If it finds a connection click it and it should show a lock unlocked and a lock locked. Maybe a silver and a gold lock. If its unlocked and its gold you can connect to it. Now you should have Wi-Fi.
Hope this helps
PS: This answer is only to connect to Wi-Fi not how to get it.