Well if everything seems to be working, you need online games now.
Some games require the use of friend codes, which means you need to add the code of your friends game, and they need to add your games code. Games that use this are Mario Strikers Charged and Battalion Wars 2.
There are also games that do not require friend codes, and simply just need you to connect to the server in the game. Games like this include Madden 08, Medal Of Honor Heroes 2 and NBA 08.
If you want to play online with friends and family, then friend codes would be your best bet, the other option is more of a random thing and you don't always know who your playing.