For sending messages (via the Wii message board (the envolope in the bottom right corner on the main screen)), you have to share "friend codes" that are found, I believe, under the "address book" within the message board. You have to have your friend's code and your friend has to have your code. Once both codes are confirmed, you can send messages to each other (like email, but will be on the message board). You can also set it up to send to/from an email address to the message board.
As for the games, there will be a "friend code" within the game itself. You have to go through the same type of procedure for each game. Some games, like Mario Kart Wii, you can share the stats about a course (who has what time and grade and who is faster than who). Games like Mario Kart Wii and Super Smash Bros. Brawl can be played "head to head" against your friends online. (SSB Brawl is slow because it's a fighting game and they have to slow it down so that the game will know whether you actually hit the other player or not.) Animal Crossing: City Folk, you can go to the friend's town after sharing codes.
As for a whole list of games that you can do this with, you might be able to find something online by searching for it. (perhaps something in the Wikipedia...I know it has a list of games compatible with the Wii Balance board under the Wii Balance board page.)
(aka Mommy_T) Central US
Zahari Skyhorn, Elite Ranger Half-Elf, Corinthium
Happiness is a butterfly, which when pursued, is always just beyond your grasp, but which, if you will sit down quietly, may alight upon you. ~Nathaniel Hawthorne
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