well, it depends on what kind of ds you have, for example;
(^ v are basically the same as the 3ds and DSi only larger.)
ok, I dont know if you are already connect to the wifi or not, but you can do that in the internet settings (in the settings) make sure you know the security code to your wifi.
now, when you go on to your Pokemon black, it should alow you to connect, if not, there may be something wrong with the wifi or, you need to check the wifi set up in ur settings, if when you try to connect to the internet on black an it tells you how to, you probably should read carefully abd follow the intructions.
I hope I helped c: