So first, try to figure out what kind of Wifi connection you have. If you have an open or WEP based connection, you can just go right ahead an pop in a game (it needs to be an online game) into the Nintendo DS conole, turn it on and go the main menu of the game.
In the main menu, look for the Nintendo Wi-Fi Connection settings. Simplest way of doing this is to select Nintendo WFC from the games main menu.
At the setup screen, click on “Nintendo Wi-Fi-Connection settings”. Well there, you need to click on the first empty slot you find. Having done that, you should let Nintendo DS search for your Wifi connection by clicking on “Search for an Access Point”.
Your Nintendo DS will search and display all wireless networks within range. Once it is finished searching, it will display the names of all the wireless networks it finds, pretty much like when you search for Wifi Networks on your computer or on your iPhone.
Look for your wireless network. If you can’t find it, you need to make sure it’s witnin range from your DS and that it’s of the right type, remember it cannot be WPA or WPA2 secured to work with Nintendo DS.
When you find your network, click on it. If it’s a blue open lock or a red closed lock, you’ll soon be on the internet. If it’s gray, it means the network security protocol is not supported.
After clicking on your network in the list, select “OK,” “Save Settings,” and then “Yes.” The Nintendo DS will run a connection test with your wireless router. If the connection test was successful, your Nintendo DS is now connected online and you can enjoy the Nintendo Wi-Fi Connection features of the game!
If you get a message saying “The connection test was not successful”, you will receive an error code. Use the error code lookup from Nintendo to see what it means. Good luck.