Well I need Jackieboy to answer this ahem jackieboy... Well... I've..

You need a Soruce of Internet Connection.

The method for connecting to the Nintendo WFC is extremely straightforward. When you purchased the game, you recieved two little booklets, the instruction booklet, and the Wi-Fi Booklet. The answer to your question is quoted from the instruction booklet:

PAGES 36-37
"Travel via Nintendo Wi-Fi Connection!
In order to play with your friends on-line via Nintendo WFC, hosts and visitors must register each other to their friend rosters..."

After registering friend codes (also explained in the instruction book):
"2. Talk to Copper
Once the name has been registered, talk to Copper and choose, 'I wanna go out' and 'Nintendo WFC.'
You will get the option to 'Check your connection setting'... Choose 'No' if you don't need to set up a new connection file. If you choose 'Yes,' then the game will automatically save and switch to the Nintendo WFC set-up screen. You can then enter or update your connection setting. (Check the Nintendo Wi-Fi Connection instruction booklet for details.)

3. Choose the name of the player whose town you want to visit
The names of players with open gates will be displayed, so pick the person whose town you want to visit.

4. Open the gate
If you are successful at communicating, the gate will open and you will be able to go out."

And, as stated earlier, you will need an internet connection.

If you have a router and your WEP key it should work.

Jackieboy Tips:

Yeah you need to either go to a place that does Wi-Fi (like a Wi-Fi cafe) or get yourself a Wi-Fi USB adapter (or something with a similar name), which will help you connect to Wi-Fi.

I decided to come on here and say this is probably the last question I'm going to answer for AC:WW, as I stopped playing the game a while ago and can't remember a lot of things >_< I'm probably going to move on to another game, either Halo 3 or Oblivion for the 360 ^_^